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LS2 Certified Horsepower—For LS2 guys

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Old 09-20-2008, 03:14 PM   #1
Marina Blue
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Default LS2 Certified Horsepower?—For LS2 guys

According to highly reliable and well placed sources within both GM Corvette manufacturing and engineering, the Corvette LS2 makes more than its rated 400 horsepower.

Over the past eight years I have gathered information supporting LS2's true SAE net horsepower rating. I have also determined the probable rating GM would have given LS2 under SAE's J2723 certification process. Before the C6 Corvette was presented to the public, Chevy apparently tested the LS2 engine using the same protocol that eventually became SAE certified horsepower. It was most likely a marketing decision not to rerate LS2 for the 2006 model year.

This information is presented in a series of documented manuscripts found in six separate posts.

I made a mistake that I cannot correct at this point. Read post #9 first and then go back to the referenced material.*

*Note--The best way to digest all of this information is to first read Post #9 (Reasons Why LS2 Should Have Been Rated At 406 Net or 411 Certified Horsepower) in its entirety. Then go back to the referenced manuscripts: Post #2 (Conversation With Tony ********); Post #3 (Corvette Quarter-Mile Factory Performance Specs); Post #4 (The effect of horsepower and weight on quarter-mile trap speeds for C6 Corvettes); Post #5 (LS2--400+ Horsepower?); and finally the unreferenced Post #6 (LS2 - LS3 Quarter-Mile Performance + LS2 Corvette at the Nürburgring and 190 MPH With Factory Stock LS2 Corvette).

Don't forget Post #11 (L-71 & L-72 True Gross & Net Horsepower) If you have an interest in how our C6 Corvette compares to the most powerful solid-lifter big-blocks of the 1960's, you won't want to miss this. True gross horsepower ratings for the L-71, L-72, L-88 and ZL-1 427s and what they rated under SAE J1349 Net horsepower specs have been determined in this treatise. This manuscript eventually became an article I wrote for Corvette Fever magazine, which appeared in the September 2010 issue on page 54. It was titled "True Power."

If you have previously read this thread, you may find that a significant amount of new information has been added.

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Old 09-20-2008, 03:19 PM   #2
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Default Conversation with Tony ********

Over a period of months, I did research to answer a question I had about how the C6 Corvette with its LS2 engine stacked up against my all-time favorite, the 1967 Corvette with L-71 engine. When I bought a new 1967 Chevelle, there was an L-71 big-block with side-pipes idling at the dealer’s lot. I never forgot that sound, or the car, so I began searching for information to see how my new Corvette matched-up. My research eventually turned into a magazine article titled “A Gross Misrepresentation” that appeared on page 78 in the October 2006 issue of Corvette Magazine. In order to make an accurate comparison between LS2 and L-71, I had to know the true horsepower rating for each. General Motors has a reputation for being somewhat conservative when advertising their numbers, at least before the advent of SAE Certified ratings.

On November 21, 2005 I called the National Corvette Museum in Bowling Green, Kentucky to see if I could find someone with knowledge of actual dynamometer test results for the LS2 engine. The Museum directed me to Dick Uber, don’t remember his title, who has an office at the Bowling Green Assembly Plant. I called his office at (270) 745-**** and was told by Mr. Uber that he didn’t have the information I wanted. He then recommended I talk to Tony ********, a “powertrain engineer” in the plant. Maybe that was tongue-in-cheek because later Tony said, "… powertrain engineer, not quite." Anyway, I called Tony at his personal cell phone number, (270) 745-****. When he answered, I was asked if I was able to wait until he finished talking with an employee. While waiting, I could hear sounds of production in the background. He was obviously working on the production floor of the plant and was a busy man. When he came back to me he said, “How did you get my number?” After I told him, "Through Dick Uber’s office", he was ready and willing to answer my questions. I asked him what the LS2 actually dyno’d and without hesitation he said, “406, 407 and sometimes 408 horsepower.” During our conversation, another employee came to him for help. Again, he asked if I minded waiting. I heard him discussing a production problem with the employee. It was evident that he held a key position at the plant. Near the end of our conversation he said, “Is there anything else you want to know?” I asked if he knew what the more recent SAE Certified rating was for the LS2 engine, but he told me that he was not aware of the Certified rating.

It was not difficult to determine that Tony ******** had and spoke with authority. I am confident that I received reliable information from someone deeply involved with Corvette production.

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Old 09-20-2008, 03:24 PM   #3
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Default Corvette Quarter-Mile Factory Performance Specs

2001 Corvette Z06, 385 horsepower LS6 – 12.6 seconds @ 114 mph

2002-2004 Corvette Z06, 405 horsepower LS6 – 12.4 seconds @ 116 mph

2005-2007 Corvette Z51, 400 horsepower LS2 – 12.5 seconds @ 115 mph

2008-2009 Corvette Z51, 436 horsepower LS3 – 12.4 seconds @ 117 mph

Conclusions based on factory performance figures:

The 405 horsepower Z06 has a 2-mph quarter-mile speed advantage over its 385 horsepower brethren. This breaks down to a one-mph benefit for each 10 horsepower in otherwise identical cars.

When comparing the performance of a 400 horsepower LS2 equipped Corvette to a 436 horsepower LS3 model, the LS3 only has a 2-mph speed advantage rather than the 3-mph advantage that 36 more horsepower should provide in identical cars. This mismatch is the result of the LS3 Corvette being 38 pounds heavier as well as horsepower ratings that were derived using different parameters. LS3 engines are rated using the revised SAE J1349 procedure where testing is done with an independent witness guaranteeing that correct guidelines were followed under the SAE J2723 verification process. LS2 was rated using the previous SAE J1349 standard. GM has consistently underrated engines by a few horsepower under the older guidelines.

Tony Holloway, a key employee at the Bowling Green Assembly Plant, told me that LS2 engines actually rated somewhere between 406 and 408 horsepower under the original J1349 method. He was not aware of ratings under the newer standard, but by using GM’s published performance data, we can calculate that LS2 would have been rated at 411 horsepower under the newer certified protocol. Here is the logic: GM’s numbers show that for an increase of 10 horsepower there is a 1 mile-per-hour increase in quarter-mile speed. The effect of increased weight for LS3 Corvettes is minus .5 mph when compared to LS2 cars, which weigh 38-pounds less. Five horsepower is needed to account for the .5 mph lost to weight so 25 horsepower is needed for the 2-mph quarter-mile speed difference between LS2 and LS3 Corvettes. If Chevrolet used a 436 hp-LS3 in performance testing, which they did, and a 25-hp advantage is necessary to account for the 2-mph speed difference, LS2 would rate at 411 SAE Certified Horsepower (436 – 25 = 411). Also, GM engines rated under the original J1349 standard gained from 1 to 29 horsepower when re-rated under the revised J1349 parameters with J2723 certification.

Chevrolet most likely underrated the LS2 for marketing purposes. The 405-HP, C5-Z06 was still the Holy Grail of Chevrolet performance in 2005, C6's first production year, so rating the new base engine at the same or higher power level would have violated the exclusiveness of Corvette’s top performing model. Also, the marketing department no doubt considered the advantages of being able to market a mid-model upgrade with 30 extra horses rather than the actual 20.

A 2002-2004 Corvette Z06 has better quarter-mile performance than a similarly powered LS2 Corvette because it is 61 pounds lighter and has less knock-retard engine management and wider, non-runflat tires. The Z06’s smaller diameter and lighter weight wheel and tire combination also results in a performance advantage.*

*Effect of wheel weight and diameter on performance--refer to the following posts:

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Old 09-20-2008, 03:29 PM   #4
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Default The effect of horsepower and weight on quarter-mile trap speeds for C6 Corvettes

My observation is that there is a one mile-per-hour trap speed difference in the quarter-mile for every ten flywheel horsepower if all other factors are equal—based on quarter-mile times for the identical, except for horsepower, 2001 (385 HP—114 mph) and 2002 (405 HP—116 mph) Corvette Z06. Variables that affect this correlation are weather and track conditions, driver skill and overall weight of the vehicle, which includes driver weight and gasoline volume. Therefore, getting a good comparison between vehicles is difficult without using controlled conditions. This is exactly what GM does when testing the performance of their cars. Corporate drivers make performance runs with all conditions, including overall weight and weather, adjusted to a standard and then the averages of numerous runs are used to come up with advertised performance figures. Using Chevrolet’s performance data for Corvettes is the only way to make a fair comparison between different models of the car.

Listed below are horsepower and weight figures as well as quarter-mile performance numbers for the C6 Z06, 2005 to 2007 model years of the base C6 with Z51 performance option, and the enhanced 2008 Corvette C6 with Z51 performance option. All horsepower ratings are derived using the SAE Certified standard, however, Certified ratings for the 2005 to 2007 cars were never published by Chevrolet. The following calculations amount to a proof of what the 2005-2007 Corvette LS2 engine would have been rated at using SAE Certified protocol.

C6 Z06 – 505 hp & 3132 lbs. (11.7 sec. @ 125 mph)

2005 to 2007 C6 Z51 – 411 hp & 3179 lbs. (12.5 sec. @ 115 mph)

2008 Z51 with NPP exhaust – 436 hp & 3217 lbs. (12.4 sec. @ 117 mph)

Comparison 1 – Z06 vs. ’08 Z51

Quarter-mile speeds are 125 & 117 mph per Chevrolet. With a 69 hp difference (505 – 436) the Z06 should be 6.9 mph faster, but is actually 8 mph faster as a result of a 85 lb. weight advantage.

Comparison 2 – Z06 vs. ’05 to ’07 Z51

Quarter-mile speeds are 125 & 115 mph per Chevrolet. With a 94 hp difference (505 – 411) the Z06 should be 9.4 mph faster but is 10 mph faster as a result of a 47 lb. weight advantage.

Comparison 3 – ’08 Z51 vs. ’05 to ’07 Z51

Quarter-mile speeds are 117 & 115 mph per Chevrolet. With a 25 hp difference (436 – 411) the ’08 should be 2.5 mph faster but is only 2 mph faster as a result of a 38 lb. weight disadvantage.

These comparisons show the effect of weight and horsepower on speed. From my calculations, every ten pounds of weight affects quarter-mile trap speed by .12955* miles-per-hour. Aerodynamics, tire rolling resistance, the probable use of rounded horsepower and speed figures by Chevrolet, and perhaps some other factors will have an affect on my mathematical equations, but I believe the results are close enough to show a fairly accurate correlation between horsepower and weight on trap speeds for C6 Corvettes.

*Calculated by subtracting expected mph from actual mph and then dividing by the number of 10 lb. units of weight difference between cars being compared. The resulting figures for each comparison are then added together and divided by 3 to get the average miles-per-hour effect on quarter-mile speed from weight in 10 pound units.

From Comparison 1 – 8 mph minus 6.9 mph = 1.1 mph/8.5 lb.=.1294117
From Comparison 2 – 10 mph minus 9.4 mph = .6 mph/4.7 lb. = .1276595
From Comparison 3 – 2.5 mph minus 2.0 mph = .5 mph/3.8 lb. = .1315789.

.1294117 + .1276595 + .1315789 = .3886501/3 = .12955 average mph change per 10 lbs. of weight

Checking accuracy of speed difference per 10 pounds of weight (.12955)

Comparison 1 – 8.5 (10 lb. units) x .12955 = 1.101175 mph difference due to weight

Calculated speed difference of 6.9 mph + 1.1 mph for weight advantage = 8.0 mph calculated speed difference.
Actual difference using Chevy’s numbers is 8 mph.

Comparison 2 – 4.7 (10 lb. units) x .12955 = .608885 mph difference due to weight

Calculated speed difference of 9.4 mph + .6 mph for weight advantage = 10 mph calculated speed difference.
Actual difference using Chevy’s numbers is 10 mph.

Comparison 3 – 3.8 (10 lb. units) x .12955 = .49229 mph difference due to weight

Calculated speed difference of 2.5 mph minus .5 mph for weight disadvantage = 2 mph calculated speed difference.
Actual difference using Chevy’s numbers is 2 mph.

The above calculations prove Certified ratings for LS2 and LS3 engines:

1. Chevrolet used a 436 horsepower, NPP exhaust equipped LS3 engine for performance testing the 2008 Corvette.

I tried using a 430 horsepower rated LS3 as well as a 400 and 405 horsepower LS2 in my calculations finding these numbers unworkable and obviously incorrect. The C6-Z06 rating of 505 Certified horsepower is not in question, but the other two were because Chevy could have used an LS3 without the NPP exhaust for performance tests and a Certified rating was never advertised for LS2. My conclusion is that the only way Chevy could have come up with their advertised performance numbers was by using a 436 horsepower LS3* and a 411 Certified horsepower LS2 during test sessions.

2. Calculations also prove that the Certified rating Chevrolet most likely would have rated LS2 engines at was 411 horsepower.

I substituted the numbers 410 and 412 in my calculations with unsatisfactory results, which again supported a 411 Certified rating for LS2.

*Two years after the LS3 engine was introduced at the National Corvette Museum’s 2007 C5/C6 Birthday Bash event, Tadge Juechter, Corvette Chief Engineer, acknowledged that a NPP exhaust (436 HP) equipped LS3 was used in performance testing to come up with a 4.1 second 0 to 60 time and 12.4 second 117 mph quarter-mile. To my knowledge, this was never publicized until 2009.

The above method can be used to determine what rating a 405 horsepower C5-Z06 would have received under the revised SAE J1349 (Certified) standard with an unknown adjustment for the advantage it has with a smaller diameter and lighter weight wheel/tire combination.

Rated under original SAE J1349 standard

C5 Z06 – 405 hp & 3118 lbs. (12.4 sec. @ 116 mph)

The C5-Z06 has a 14 pound weight advantage (3132 – 3118) over the C6-Z06.

Multiplying 1.4 (14/10) ten-pound units times .12955 (average mph change per ten pounds of weight) equals .18137. This translates to a .2 mph advantage for the C5-Z06 because of weight.

The C6-Z06 with its LS7 engine is 9 mph faster than a LS6 equipped C5-Z06 (125 – 116). However, the C5-Z06 has a .2 mph advantage because it is 14 pounds lighter in weight. That .2 mph weight advantage must be added, resulting in a 9.2-mph speed differential between the two cars if they were equal in weight. The C6-Z06 must have 92 more horsepower (9.2 x 10 hp) than a C5-Z06 to be 9-mph faster in the quarter-mile. By subtracting 92 from LS7’s rating of 505 Certified horsepower we come up with a 413 Certified horsepower rating for the LS6 engine. This figure must be adjusted for the performance advantage--approximately one-mph better than a C6 corvette in the quarter-mile--that results from the smaller diameter and lower weight wheel/tire combination on the C5-Z06.

We can prove that the calculations are correct by making a comparison with the LS2-C6 Corvette considering that 10 horsepower is needed for a one mile-per-hour speed advantage in the quarter-mile after adjusting for unequal weight.

Base LS2-C6 – 3179 lbs.
C5-Z06 – 3118 lbs.
Difference 61 lbs.

6.1 ten lb. units x .12955 = .790255 = .8 mph advantage from weight

C6 quarter-mile speed of 115 mph + .8 mph for C5-Z06 weight advantage + .2 mph for LS6’s
2 horsepower advantage = C5-Z06 quarter-mile speed of 116 mph

Certified Ratings for Corvette engines

LS7 with dual-mode exhaust – 505 horsepower (per Chevrolet)
LS3 with dual-mode exhaust – 436 horsepower (per Chevrolet)
LS3 without NPP exhaust – 430 horsepower (per Chevrolet)
LS6 (405 hp--original J1349) – 413 minus 8 to 10 horsepower (Calculated)*
LS2 (400 hp--original J1349) – 411 horsepower (Calculated)

*Unlike C6 Corvettes, all of which have 19-inch diameter rear wheels with EMT (run flat) tires, the C5-Z06 has 18-inch rear wheels and lighter weight, non-EMT tires. Both wheel diameter and weight will affect quarter-mile performance as well as rear-wheel-horsepower on an inertia type chassis dyno. When compared to the C6, a C5-Z06 benefits from its wheel/tire combination. As a result, my calculated 413 horsepower is too high for the LS6 and its Certified power is probably much closer to the original 405 rating. Corvette Forum member TTRotary calculated that a C5-Z06’s smaller diameter wheel is worth about 9.5 horsepower at the rear wheels. Refer to these two posts:

Last edited by Marina Blue; 12-31-2014 at 11:50 AM. Reason: Calculations prove 411 hp LS2 and 436 hp LS3 used in testing
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Old 09-20-2008, 03:38 PM   #5
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Default LS2--400+ Horsepower?

At the time I wrote this, Jim Schindler had the top LS3 number on “The List.” Jim is always reliable so I chose to stick with his numbers because I also used his chassis dyno information.

LS2 – 400+ Horsepower?

Chevrolet gives Corvette LS2 engines a 400 horsepower rating at 6,000 rpm and LS3 engines a 430 horsepower rating at 5,900 rpm. When equipped with the optional NPP exhaust system, LS3 is rated 436 horsepower at 5,900 rpm. LS3 was rated using the updated SAE J1349 procedure and then certified under SAE J2723. Officially, LS2 was only rated under the previous SAE J1349 standard, however, GM engines that were rated under both SAE procedures gained from 1 to 29 horsepower under the newer certified method. The Cadillac STS-V with its Northstar V8 gained 29 horsepower when re-rated under the new protocol.

According to Chevrolet testing, a LS2 equipped C6 Corvette with Z51 performance option and manual shift is able to go from 0 to 60 mph in 4.1 seconds and the quarter-mile in 12.5 seconds at 115 mph. Chevrolet states that the LS3 Corvette with Z51 option and manual shift is able to run from 0 to 60 mph in 4.1 seconds and the quarter-mile in 12.4 seconds at 117 mph. Corvette forum member, Jim Schindler, owned both LS2 and LS3 equipped cars and ran the quarter-mile in 12.49 seconds at 114.9 mph in his 2005 LS2, manual shift, Z51 coupe and 12.409 seconds at 114.7 mph with his 2008, 436 horsepower LS3, manual shift, Z51 coupe. However, Jim had a top speed of 117.03 mph on one of his seven runs at Houston Raceway Park. Overall, it looks like he matched the Chevy performance spec with both cars. Chevrolet performance numbers are derived from an average of numerous runs made under controlled conditions and then adjusted for standard day temperature and density altitude (DA). Also, corporate professional drivers drive the cars. All of this results in a consistency difficult to duplicate outside of corporate testing.

Schindler had his LS3 Corvette tested on a chassis dynamometer by MTI in Houston, Texas. The best dyno run resulted in SAE corrected numbers of 390.5 horsepower and 380.5-lb.ft. of torque. Jim asked what a stock LS2 rates on MTI’s chassis dyno. MTI pulled a typical stock LS2 dyno sheet showing 353.7 horsepower and 354.3-lb.ft. torque. The difference between Schindler’s LS3 and the LS2 was 36.8 horsepower and 26.2-lb.ft. torque.

Observed chassis dyno numbers for factory stock, manual shift, NPP exhaust, LS3 Corvettes have ranged from 374 to 399 horsepower. Numbers for factory stock, manual shift, LS2 Corvettes range from 338 to 365 horsepower. It is impossible to tell where most numbers are concentrated within the range because of unreported results and my inability to gather all chassis dyno figures that were reported. When the range varies by at least 25 to 27 horsepower it becomes apparent how unreliable chassis dyno numbers are as a predictor of true engine horsepower. These variations are due to dynamometer type, dynos being out of calibration, operator input, tire pressure, engine temperature, hood open or closed, correction factor error, fuel octane, drivetrain wear, tire size and wheel weight, effect of feedback-spark-control on degree of timing retard, etc. It is obvious that using chassis dyno numbers to back calculate true engine horsepower is unreliable at best.

Range of LS2 rwhp witnessed by LG Motorsports--See this post:

Range of LS3 rwhp--See the following posts:

Using a percentage such as 15% to calculate loss of power between the flywheel and rear wheels is somewhat common even though it is incorrect. Calculating drivetrain loss between cars with different horsepower ratings has constant, linear, and exponential components but is closer to a constant number assuming peak power occurs at equal rpm and cars are equipped with the same transmission, differential, wheels, tires, tire pressure, etc. and the effects of knock retard are either not present or equal. Beginning with the C4 Corvette and continuing with C5 and C6 Corvettes with T56 transmissions, the commonly accepted drivetrain loss was 60 horsepower or 15%. Those losses are no longer valid for LS3 Corvettes because of increased drivetrain efficiency and less intrusive engine management.

Higher rpm results in more friction loss, especially when the whole drivetrain is involved. When comparing cars where peak power occurs at different rpms, friction loss can be adjusted in a strict linear relationship—the predominant term when comparing loss at varying rpms. This results in close to one horsepower advantage at the rear wheels for the LS3 Corvette. A 100 rpm friction loss based on a 60 horsepower drivetrain component (difference between flywheel and rear wheel horsepower, otherwise the complete drivetrain) is calculated as follows: 6,000 rpm – 5,900 rpm = 100/6,000 = 1.67% and 60 x 1.67% = 1.002 horsepower lost to additional friction.

Corvette changed from the Tremec T-56 to TR-6060 manual transmission in 2008 Corvettes. That transmission has internal changes which result in a different friction factor than the T-56. A statement that Dave Hill made during a Corvette Action Center interview with Hib Halverson indicates the effect drivetrain components can have on performance: “There's three different types of gear rattle, neutral, shutdown and driveaway. We had some hardware that was going to get rid of all three, but we decided to reverse one of them because the solution was costing too much acceleration. That was a dual-mass clutch and it would have eliminated all of the driveaway rattle but it would have cost us 2/10ths sec. in 0-60. We said, 'Even for driveaway gear rattle, that's too much of a performance price to pay because it was a significant amount of what we gained with the 400hp.' So we eliminated the neutral gear rattle, the shutdown gear rattle and got more than half of the driveaway gear rattle. That is the only thing that I wanted to get that I didn't.”

Wheel weight and new differential gear oil also become factors in drivetrain power loss. The new forged wheel option is reportedly from 1.6 to 3 pounds lighter in weight for the front and from 2 to 4 pounds lighter for the rear wheels. This results in less rotational mass, which gives an advantage on an inertia type chassis dyno. For model year 2008, Corvette differentials were filled with a new gear oil (Dexron LS Gear Oil 75W-90) resulting in less power lost to friction in this drivetrain component.

It is not hard to understand why LS3 Corvettes are experiencing less parasitic drivetrain losses taking into account a new TR-6060 transmission, peak horsepower occurring at a lower RPM, lighter weight forged wheels and a new gear oil with better lubricating properties.

I had the pleasure of talking to a Tremec transmission representative at the 2013 Corvettes at Carlisle show. He verified that the TR-6060 transmission was not only stronger than the T-56, it is also more efficient and presents less parasitic losses in the drivetrain. I specifically asked him if that included the straight-through 4th gear—the gear used during chassis dyno testing. His answer was: “Yes...there is less 4th gear friction in the TR-6060 than in the T-56, resulting in more power to the wheels."

GM publication, Corvette Quarterly, had an article titled “Takin’ It to the Limit” in the Winter 2008 issue. In this case “Limit” did not refer to top speed performance, but to getting the best gas mileage possible in a base model LS3 Corvette. The fact that the car traveled 549 miles on one tank of gas with an average fuel economy of 30.6 miles-per-gallon is not what attracted my attention. There was one small sentence that stood out like a Boeing 747 on a radar screen—“Continual reductions in internal friction also pay dividends at the fuel pump.” The article also stated, “A third reason for the Corvette’s efficiency is its powertrain. Taken as a complete unit, it’s hard to beat.” Those sentences amount to a subtle statement that the LS3 drivetrain is more efficient than the previous LS2’s. Tadge Juechter, Corvette Chief Engineer, talked to the author before the article was written. I’m sure he explained some of the finer details of drivetrain efficiency.

Along with less power lost to knock-retard engine management under extreme operating conditions, reduced drivetrain friction is another factor in LS3’s apparently higher chassis dyno numbers when compared to an LS2 that is rated at 406 Net or 411 Certified horsepower.

Calculating Drivetrain Power Loss For LS2 and LS3 Corvettes

Average rear-wheel-horsepower (based on low and high numbers, not the full range)
Note: These numbers do not represent an average of all chassis dyno numbers but should be ballpark figures.

LS2 rwhp – Range 338 to 365 Average – 351.5 rwhp
LS3 rwhp – Range 374 to 399 Average – 386.5 rwhp

Power lost in drivetrain

LS2 – 400 SAE Net hp minus 351.5 rwhp = 48.5 horsepower (12.125% Drivetrain Loss)
LS2 – 406 SAE Net hp minus 351.5 rwhp = 54.5 horsepower (13.42% Drivetrain Loss)
LS2 – 411 Certified hp minus 351.5 rwhp = 59.5 horsepower (14.48% Drivetrain Loss)
LS3 – 436 Certified hp minus 386.5 rwhp = 49.5 horsepower (11.35% Drivetrain Loss)

LS2 Corvettes are exhibiting a loss of about 10 more SAE Certified horsepower--due to "knock retard" engine management and drivetrain parasitic losses--than LS3 Corvettes. Loss difference will probably change somewhat if a more complete average set is used.

LS2, with a 54.5 horsepower drivetrain component, loses .91 more horsepower to friction as a result of peak power occurring 100 rpm higher than LS3.
(54.5 hp x 1.67% = .91015 hp)

LS2, with a 59.5 horsepower drivetrain component, loses .99 more horsepower to friction as a result of peak power occurring 100 rpm higher than LS3.
(59.5 hp x 1.67% = .99365 hp)

Supporting posts:

Why LS2 Is Not Perceived To Be The Rocket Ship It Really Is

Most performance cars exhibit the feeling of “coming-on-the-cam,” or that someone just turned on the afterburners. A Corvette LS2 does not feel that way because its power curve is smooth and linear. LS2 has great torque and power at low as well as high rpm.

Hib Halverson, writing for Corvette Action Center's website, did a number of in-depth articles about the C6 Corvette when it was a new model. In an interview with Jordan Lee, GMPT Small-Block Chief Engineer, who worked on the LS2 program, Lee said, “At the bottom end, the LS2 is so much fatter than the LS6. There is one thing you gotta be cognizant of: a lot of people think, when they drive very high-performance sport cars, they’re tuned only for high rpm. People perceive that because the bottom end is so weak. You step in the throttle at low rpm and the engine’s flat, but then, all of a sudden, it feels like it’s coming on the cam.”

“The LS2 has a fat, broad torque curve so it’s very satisfying down low, but you never have that rapid, flip-the-switch type of feel at higher engine speed. For my taste, and I think the majority of sports car drivers agree, it’s more satisfying to have all that responsiveness and still have all the top end.”

Halverson’s response, “I’m with Jordan Lee on the “satisfying” thing (and the C6’s acceleration numbers are with him, too), but I’m not so sure all Corvetters will agree with us because the erroneous belief that “comin’ on the cam” is demonstrative of a powerful engine is so pervasive amongst urban legends in the car hobby. Reality is: if a normally-aspirated engine really has that on-off or on-the-cam feeling, it’s either a race engine or a production engine with poor air flow management, either of which kind of suck on the street.”

“Conversely, the LS2’s bulked-up, low-end adds to its LS6ish top-end to make a torque curve that’s flatter than freakin’ Kansas. Its lack of peakiness makes the car easier and more fun to drive. It idles nicer than an LS6 and has a tiny edge in throttle response. All this comes under the heading of “refinement.”

Jim Schindler mentioned this a number of times when comparing his 2005 LS2 Corvette to a friend’s modified C5 Z06: “When I got my first C6, a friend who has a 2002 Z06 with headers, tune, etc. (382 rwhp) came over and we drove each others cars. His FELT like it would run off and leave my C6 for dead. But a funny thing happened side-by-side. Even with his mods, they were damn near equal—his only advantage was slight at higher speeds.”

TTRotary had a similar experience: “When I bought the C6, I was pretty sure it was noticeably slower than my Z. Since I still had it, I got a friend to drive and we did some highway pulls from 45 or so. To my surprise, the C6 was right there with the Z through 120. It was interesting, the C6 would pull on the Z at the low end of each gear and the Z06 would catch it back on the top end of the gear. The C6 was Z51 so same gearset. As an experiment, we swapped rear wheels. The Z could no longer pull. So I'd conclude that the 6.0L is a pretty stout motor if it can move a heavier car that well despite have same HP. Also, the C6 tune, as you know, is a dog. After Shawn's tune, my LS2 has that same razor-sharp response the LS6 had.”

Shortly after LS2’s introduction in the C6 Corvette, Motor Trend magazine made a direct comparison between LS2 and LS6 engines. Identical Cadillac CTS-v cars, with different engines, were used in testing. The LS2 car out-accelerated the LS6 Cadillac, leading the magazine to conclude that LS2 was the stronger engine. This test was reported by Motor Trend in the front, News section of an issue I no longer have, and therefore am not able to reference. But, the result of their test was mentioned in the October 2005 issue on page 102 in the CTS/CTS-v section: "The high-performance CTS-v gets a new V-8 engine that still produces 400 horsepower, but now propels the car to 60 mph even quicker."

LS2 Corvettes do not feel as fast as they really are.

Another problem the LS2 has is spending too much time in low, “knock retard,” timing tables. Corvette LS2 engines have a 10.9:1 compression ratio and are designed to run on 93 octane gas in optimal conditions.

Hib Halverson wrote the following: “General Motors’ 2004 media Product Information Guide, or PIG (“media pig”-hidden meaning, perhaps?) says 93-octane gasoline is “recommended” for use in Corvettes. Owner’s Manuals for ’04 say to use ”…91-octane or higher for best performance.” While there seems to be a difference between what GM tells media and what it tells owners (certainly not the first time that’s happened), most people will run LS2s on whatever premium unleaded they find. Generally, this means 93-octane along the East Coast and parts of the Midwest and 91-octane in most of the rest of the country.”

“LS2, like all Corvette engines since 1982, has computer-controlled spark timing and part of that is a feedback loop which eliminates detonation which can damage the engine. When the knock sensors signal the engine controller that detonation is occurring, in milliseconds, the controller retards timing—we call this “knock retard”—until detonation stops and, once it stops; timing is restored. This feedback process goes on constantly such that spark timing is always at the optimum level for best performance, highest fuel economy, lowest emissions and the octane of the gasoline being used.”

“In nominal atmospheric conditions, 93-octane is adequate for the LS2 to perform optimally with minimal knock retard to control detonation, however, some of my chassis dyno testing of pump gasolines leads me to speculate that, to run detonation-free under the worst conditions, i.e.: wide-open-throttle, heavy load, low humidity, sea level (or near so) pressure, high intake air temperature and high coolant temperature—the LS2 probably needs about 95-octane.”

“With the engine calibrated for 93-octane, that extra last bit of performance during severe duty requiring perhaps as much as 95-octane, Corvetters in a fair amount of the country stuck with 91 and a few errant owners trying to use regular; feedback spark control and knock retard are what allows the engine to produce highest-performance on good gas but not be damaged by detonation when running on gasoline of less than 93-octane.”

Corvette forum member, TTRotary, commented on the effect knock retard engine management has on his LS2 Corvette in hot weather—“Now for the caveat: for some reason (perhaps aggressive engine management due to high compression ratio), the LS2 in the C6 just falls apart on a hot day. 68-75F, the thing is a monster—I like it better than the LS6. But give it 95F and turn on the AC, and it becomes a DOG.” He also commented on knock retard being mistaken as torque management (TM)—“The good news is I have never encountered TM on my car, even when temps are cool and I rip the 1-2 shift hard. Maybe engine management is what people have confused with TM. If ever a car needed cold air intake and a tune, it’s this one.”

Corvette forum member, Yawlak80-86, made excellent posts on octane requirements for LS2: and He said, “The problem is especially bad with LS2s as they have too much timing combined with too high a compression ratio from the factory. They spend most of their time on the low tables when using 91 and still ping. . .When I go to the track, I run a blend of 100 octane race fuel w/ 91 octane pump gas making at least 95 octane so I can run adequate timing." He also mentioned the LS3—“The owners manuals are not gospel. LS3s have a slightly lower compression ratio than the LS2 and LS7. They also have much better heads than the LS2 (perhaps the quench zone is relocated in the cylinders as a result—I’m not positive). Perhaps these are some of the reasons they say the LS3s are good with 91-octane but I can tell you with certainty, they are not, at least not in my neck of the woods. I can also tell you that I had no pinging issues on the East Coast with premium top tier fuels, (except for Shell).”

Corvette forum member, Tommy D, made a post which supports the contention that knock retard engine management is not as intrusive on the LS3—“Remember that torque management cannot be tuned out on launch and is not as intrusive on the later C6s.”

On page 6 of “C6 Naked and Exposed – The Sequal; Finally . . . We Drive It!!!," GMPT engineer Jordan Lee states, “When you bump the compression, you need better combustion efficiency, so you're less prone to knock (underline my emphasis); but if you do get knock; you need a control system which can react very quickly so that it’s unobtrusive to the driver.”

On page 5 of “Ruthless Pursuit of Power: 2008 Edition,” Hib Halverson had this to say about LS3 combustion quality: “The best combustion quality occurs when the air fuel mixture in the chamber is distributed uniformly, or is “homogenous”, throughout the chamber. The process of becoming homogenous, or as close to it as possible, occurs in the latter stage of the intake valve event and continues once the valve is closed and the piston starts upward. Not only does the upward piston movement compress the air-fuel mix but it also causes it to swirl and tumble and that further mixes it up making it more homogenous. The LS2/LS6 chamber had great swirl but not very good tumble. The air fuel mix needs to be doing both if the goal is homogeneity right when the spark comes.” A bulge added to LS3’s combustion chamber caused the mixture to tumble as well as lowering the compression ratio.

Combustion quality along with a lower compression ratio allows LS3 engines to spend less time in “knock retard” than LS2. This is why LS3, in combination with a somewhat more efficient drivetrain, shows better numbers on many chassis dynos than an LS2 engine with only 20 less horsepower.

Anthony @ LGMotorsports did a back-to-back comparison of a LS2 Corvette, LS3 Camaro and a 5.0 Mustang. Here it is:
LS3 Camaro Max power was 374.35 RWHP; LS2 Corvette was 358.99 RWHP. Difference is 15.36 HP. Camaro LS3 Certified HP is 426; LS2 Certified HP should have been 411. That is a 15 HP difference. I believe a back-to-back comparison means all dyno runs were done at the same time. It looks like LS2 was on the right timing table.

LG Motorsports’ back-to-back comparison shows that the power differential between LS2 and LS3 is greater in midrange rather than at peak power rpm levels. LS3 surpasses the 15 horsepower difference at about 3500 rpm . This continues until peak power is reached at 5900 and 6000 rpm where there is a 15 horsepower difference. The chart also seems to show LS3 losing power more rapidly than LS2 after peak power levels are reached. Projecting LS3’s power curve to 6600 rpm, it looks like LS2 and LS3 power levels will be practically the same. But don’t forget, this is for the 426 HP LS3, not the 430 HP Corvette LS3.

GM’s Corvette power and torque chart shows that, unlike LG Motorsports, the greatest power differential between LS2 and LS3 is reached at peak levels. The GM chart can be seen here in post #1: This chart shows that LS2/LS3 power and torque are nearly the same until about 3500 rpm, where LS3 starts climbing at a faster rate. LS3 power and torque change their angle of ascent, whereas, LS2 continues rising at a steady rate. LS3 acts more like an LS6, so “coming-on-the-cam” is a noticeable sensation.

How LS2 made 20+ HP over ’01 LS6 and LS3 made 20 HP more than LS2

Dividing ’01 LS6’s 385 horsepower by its 346 cubic-inches results in 1.1127 HP per cubic-inch. Multiplying that figure by LS2’s 364 cubic-inches results in 405 HP. Both engines use the same cylinder heads and camshaft, but LS2 has a power-increasing higher compression ratio (10.9:1 advertised – 10.87:1 actual) than LS6 (10.5:1).

LS2 has a single catalytic converter mounted right after each exhaust manifold rather than the close-coupled converters—known as pups—that were combined with the under-car converters on the ’01 LS6. Having one converter on each side reduced back pressure by 2-inches of mercury (16%), which on its own is worth about five horsepower. Along with exhaust manifolds that flow 4% better and exhaust pipes with smoother bends, LS2 benefits by having longitudinally-mounted mufflers with larger internal volume resulting in 10% less restriction than the transverse mufflers with four, 90-degree tube bends that were mounted on all C5 Corvettes. These improvements resulted in a total of 20% less back pressure in the exhaust system.

A redesigned induction system (air box and duct) resulted in 31% better airflow. Most of this increase was the result of C6 Corvettes becoming both front-breathers, air entering through the grill, and bottom-breathers, air entering from the bottom of the car—split 60% front; 40% bottom. Base C5 Corvettes were bottom-breathers only, but the Z06 LS6 had additional air ducted directly to the air-filter box from openings in the front fascia—C6 air flow was an improvement over the Z06. LS2 uses the same mass-air-flow sensor (MAF) as the '02 to '04 LS6, but with the honey-cell flow straightener found in the '01 LS6. Throttle body size went from 76-mm on the LS6 to 90-mm on LS2. Fuel injector capacity increased to 32.5 lb/hr. (4.1 g/sec.) from LS6's 28.5 lb/hr. (3.6 g/sec.).

LS2’s intake manifold was produced using the vibration welded process. It is glass-filled and made out of Nylon 6 rather than Nylon 66, which was used in LS6’s lost-core-process manifolds. The bell-mouth is larger and runner geometry has been optimized for a six-liter engine. The combined result of all intake/induction system improvements is an air flow increase of 15%.

Vibration welding has resulted in seams that allow crosstalk—air passing between runners—which is detrimental to smooth air flow and results in some lost power. GM went back to the lost-core process for the LS3 engine but used Nylon 6. John Rydzewski, Assistant Chief Engineer for Small Block Passenger Engines: “A vibration-welded intake has different shells. One port can be a combination of an upper portion and a bottom portion with the runners welded together on the side. It’s a pretty good seam, but there might be a little crosstalk (port-to-port leakage) which can rob you of some power. We had seen that in some applications, so we went to a lost-core intake (on LS3).” Vibration welding was also used in the production of LS7 intake manifolds; however, at some point the seams were sealed to prevent crosstalk. I doubt that sealing was ever used on LS2 intakes.

LS2’s pistons have a true flat-top design with all three rings having lower tension than LS1 and LS6 rings. Lower tension reduces friction to free up horsepower. The pistons also have full floating wrist pins that help reduce the piston slap noise that’s common on Generation III engines (LS1, LS6). Gen IV engine blocks (LS2, LS3) have siamesed cylinder bores, meaning that a water slot between bores is unnecessary for adequate cooling and that all bores have a solid, uninterrupted connection. This resulted in a stronger block that is less prone to heat distortion in the cylinders. Less bore distortion means less friction and pumping losses.

Both intake and exhaust airflow are better on LS2 Corvettes than the 2001 LS6. LS2 uses the same cam and heads as the ’01 Z06. With a higher compression ratio, 18 more cubic-inches, induction/intake and exhaust flow better than 2002 to 2004 LS6 engines and various internal modifications that decreased friction and pumping losses, LS2 should have been rated at the 406 or 407 SAE net horsepower that Tony Holloway told me LS2 engines produce. In applications using the LS6 385-horse cam, torque equals horsepower, so LS2 torque should match its horsepower rating.

LS2 never received an official certified rating under the new, for model year 2006, SAE J1349 procedures. But GM, knowing that the new protocol was coming, rated LS2 using the new methods long before the engine received its official 400 horsepower rating. Under SAE certified protocol, LS2 rated between 410 and 415 horsepower. If the new rating system had been ready for the 2005 model year, LS2 would NOT have been rated at 400 horsepower.

The 2002 version of LS6 and 2008 LS3 made 20 horsepower more than their predecessors. Both engines used the same cam intake profiles, but LS3’s exhaust profile is the same that was used in the ’01 LS6 and LS2 cams. Along with more aggressive cams, power gains were derived from exhaust back pressure reductions on the '02 LS6 and better flowing heads on LS3.

The following six paragraphs were taken from an article titled 2002 LS6 Engine – The Ruthless Pursuit of Power: The Sequel by Hib Halverson, from the January, 2002 issue of GM High-Tech Performance magazine.

According to LS6 camshaft engineer, Jim Hicks, in comparing the ’01 LS6 cam to the ’02 cam: “You can do a direct A/B comparison and there’s an easy 8-10 HP there, whether you change the back pressure or not. There are other changes in the ’02 package—exhaust system and induction system—which increase the power more. The overall power increased about 20 HP and the cam was half of it. Again, that’s because it’s a short-duration design with low overlap so it’s not really affected that much by back pressure.”

Corvette Chief Engineer, Dave Hill said, “We never set out to obsolete the 2001 LS6. The horsepower increase was possible only after we completed a lengthy development of a new catalyst. I want to set the record straight: the 2001 was the best Z06 we could possibly make and 2002 is better because new catalyst technology let us get the back pressure down, increase the breathing and make that power increase.”

Assistant Chief Engineer for Gen III Passenger Car Engines, John Juriga, added, “In 2000 we had to meet the LEV standard here in California, so we added close-coupled converters up front on the California package, our ‘pups’ as we call ‘em. In 2001 we carried those pups across the board, including on the LS6. Even while we were implementing that, we were working on a design that would eliminate those pups. This reduced back pressure by two inches of mercury. On its own, that was worth about 5 HP. That seems not much, but if you reduce back pressure by even small amounts, you can make a bigger gain with improvements on the induction side, especially with the cam.”

More airflow from the new cam and less back-pressure from the new cats drove some other improvements on the induction side. For MY02, LS6 gets a new air filter assembly. It’s similar to the ’01 unit in that it has an additional air intake opening on its cover, but the extra opening is larger. GM also did what GMHTP readers have been doing for years with MAFs--remove the air flow straightener screen. This allowed for a less restrictive path through the sensor.

There were no changes to either the LS6’s intake manifold or its cylinder heads. John Juriga: “The intake manifold was already pretty darn good. We designed it to handle additional flow rates and not require retool the very next year because composite intakes are very expensive to retool and develop. We made sure it would flow more air than we needed in the first year. The same was true with the heads.”

A change in engine air flow significant enough to provide 20 more horsepower also demanded a small change in the engine’s fuel and spark curves. This was done with slight changes in the PCM calibration. There was no change in injectors or fuel pressure.

Low hanging fruit had already been picked for the LS2 engine to come up with 20+ more horsepower than the 385-HP LS6, so LS3 needed a significant upgrade for an equal increase in power. LS3 had no changes in the exhaust system after the cylinder head exhaust ports and there wasn't as great a difference on the induction side before air entered the intake manifold. LS3’s intake manifold was again made using the lost-core process and flowed 2-3% better than the LS2 intake. To add 20 more horses, there had to be a major upgrade in the cylinder heads along with the new cam. LS3 did not have the advantage of eighteen more cubic-inches (5.2% more than LS6) and the higher compression ratio that LS2 had over the LS6. LS3 was only twelve cubic-inches or 3.3% larger than LS2 and its compression dropped from LS2’s 10.87:1 to 10.7:1.

A Corvette Action Center article titled Ruthless Pursuit of Power: 2008 Edition by Hib Halverson describes the improvements that increased LS3 power.

Assistant Chief Engineer for Small Block Passenger Engines, John Rydzewski, talks about improvements in the intake manifold: “We also reshaped it for better flow. Yoon Lee, who’s been on the program for a few years, did the development. Compared to LS2, he reduced restriction by 2-3% at 13.5mm lift. It’s just a smoother path, right down to the head.”

Compared to LS2/LS6 cylinder heads, LS3 heads flow much better. According to Lou Oniga, Design Responsibility Engineer (DRE) for Small-Block Cylinder Heads, “The flow numbers are (average) 17% improvement on the intake and 6.2% on the exhaust.”

LS3's camshaft was improved with a 405-HP, LS6 intake lobe profile--exhaust lobe profile from the 385-HP LS6/LS2 cam was retained.

LS3 fuel injectors come from LS7 and flow 5-gram/sec.--LS2 injectors flow 4.1-gram/sec. The throttle body carries over from the LS2. There are no functional changes to the positive crankcase ventilation (PCV) system. The induction system ahead of the throttle body is from the Z06, but with some quarter-wave tuners added to attenuate certain frequencies of intake noise. Overall, induction/intake restriction has been reduced by 10% (Corvette Quarterly, Fall 2007, page 50). The exhaust manifolds are similar to the units introduced in 2005 on LS2, but have a slight change in each exhaust runner where it bolts to the head to match the revised exhaust port exits. Exhaust pipes after the manifold are the same as the LS2, but when the NPP option is included, a flap in each muffler opens allowing exhaust gases to flow more freely...adding 6-horsepower.

There are improvements in the LS3 block: Main bearing webs are about 20% stronger and windows, which enhance “bay-to-bay breathing” in the interest of oil control and reduced parasitic loss, have been somewhat enlarged. LS3's ring package has once again been changed: The top two compression rings have the same tension as LS2 rings; the bottom, oil ring tension was increased. All rings have a .25-degree increase in grove tilt. Increased grove tilt and oil ring tension improved oil control, but more tension adds friction, which is a drag on power.


LS2 vs ’01 LS6 (Corvette: Sports Car Super Star by the Auto Editors of Consumer Guide, 2005, Publications International, Ltd., page 391) (The Complete Book of Corvette: Every Model Since 1953 by Mike Mueller, 2006, Motorbooks – MBI Publishing Company, pages 315 & 328)

LS2 Exhaust System – New exhaust manifold is capable of 4% better flow; back pressure reduced by 2-inches of mercury (16%) with a single catalytic converter attached to the exhaust manifolds rather than close-coupled pup-cats and under-car converters; smoother exhaust-pipe bends; 10% less back pressure with the elimination of four, 90-degree tube bends at mufflers and less restrictive larger internal volume mufflers. In total, the reduction in exhaust back pressure is 20% over the 2001 base system.*

LS2 Intake System – Significant improvement was made because C6 Corvettes became both front- and bottom-breathers. Intake manifold: runner geometry optimized for six-liter displacement; larger bell-mouth; crosstalk causes slight power loss. Throttle-body size increased from 76-mm to 90-mm; induction system (air box and duct) redesigned for lower restriction—31% lower restriction than LS1 induction system.* Overall, intake/induction system airflow has been improved by 15%.

*Note: Beginning with the 2001 production year, LS1 and LS6 engines used the same intake and exhaust manifolds, MAF sensor, and throttle body. These improvements were worth an added ten horsepower to the LS1. For model-year 2000, the addition of pup-cats to California Corvettes resulted in a loss of five horsepower, which means these cars actually made an unadvertised 340 horsepower. The same power reduction would have happened to all 2001, LS1 Corvettes if it hadn’t been for the intake and exhaust upgrades. Chevy never publicized the California power loss and didn't rerate the engine until 2001 (350 HP).

Cylinder heads and cam – Heads are same as 2001 to 2004 LS6; cam is same as 2001 LS6

Engine – Compression ratio increased from 10.5:1 to 10.87:1; displacement increased by eighteen cubic-inches or 5.2%; lower tension piston rings free up horsepower; siamesed bores result in a stronger block and cylinders with less bore distortion, friction and pumping losses.

LS3 vs LS2

LS3 Exhaust System – no change from LS2

LS3 Intake System – Intake manifold restriction reduced by 2-3% and made with lost-core method—no lost power; throttle-body same as LS2; induction system same as Z06, but with quarter-wave tuners; overall induction/intake restriction reduced by 10%.

Cylinder heads and cam – Significant cylinder head upgrade with average intake flow increased by 17% and exhaust increased by 6.2%; cam intake profile same as ’02 LS6, exhaust profile same as LS2.

Engine – Compression ratio dropped from 10.87:1 to 10.7:1; displacement increased by twelve cubic-inches or 3.3%; reduced parasitic loss from increased bay-to-bay breathing; a .25-degree increase in piston-ring grove tilt and higher-tension oil rings resulted in better bore sealing and oil control, but increased power-robbing friction.

LS2 improvements resulted in a 21 or 22 horsepower increase over the 385-HP LS6 and LS3 improvements resulted in a 20 horsepower increase over LS2. Compared to LS2, LS3 had no increase in exhaust flow after exhaust gases left the heads and induction/intake flow restriction was reduced by 10%. LS3’s cam was not as significant an improvement as the 405-HP LS6 cam was over the 385-HP version. The 405-HP LS6 cam gained from 8 to 10 HP, so in my opinion, LS3’s cam gained somewhat less. To get another 11-14 horses, LS3 needed a major flow increase from its heads (17% intake - 6.2% exhaust), especially considering that LS3's compression dropped compared to LS2 and it had 36.5% less increase in cylinder volume in comparison to LS2’s increase over LS6. LS2's largest power gains came from increases in compression and cubic-inches, but significant air-flow upgrades--15% on the intake side and 20% on exhaust--were the drivers of more power and torque at both low and high rpm levels without using a bigger cam.

During engine development, Corvette's Chief Engineer and Vehicle Line Executive, Dave Hill, wanted LS2 power to be where the Z06 LS6 was (405 HP) without the premium hardware (longer, hollow-stem valves with potassium-sodium filled exhaust stems), although LS2 did get the stiffer '02 - '04 LS6 valve springs for high rpm stability. I bet he was satisfied with the outcome. GMPT’s Executive Director of Engine Engineering, Sam Winegarden: “Chief engineer Dave Hill said he would really like to take all standard Corvettes to where the Z06 was, and we said that jived with where we saw our competitors, from an engine perspective, going in terms of horsepower. We continually benchmark our engines against our competitors and look at the trends.” (Corvette C6 by Phil Berg, 2004, Motorbooks International, page 63)

Jim Hall, owner of Corvette Forum vendor, Halltech Systems, LLC (Halltech), started a thread with an interesting post on 4/29/2004 that was ahead-of-the-curve. I was not able to find his original post, but it was quoted in another post: (The beginning of Jim's thread was deleted. If you look at post 1 and 2, it becomes clear these were not the first two posts of the thread. They were made on 3/19/05, almost a year after the thread was started on 4/29/04, and then renumbered. Sometime after the original thread began, GM expressed great displeasure with a vendor's post on this forum. It could have been this one--my memory of the details has faded with time. Obviously much of the original thread was eliminated, so we only have the following quote from post #9 as evidence of Jim Hall's original post.)

Originally Posted by Jim Hall

The C6 is actually 420+ HP.

Why do I suggest that? Three years ago, I posted a thread on the corvetteforum, with a poll asking how many folks would purchase a C5 Coupe with a LS6 option. There were many interested members.

Some quoted Dave Hill as stating that he would never put the Z06 motor in the Coupe or Convertible.

The C6 is just that and more.

400 HP is ridiculous for the amount of internal changes found in the LS2. It is actually a hot rod Z06 motor in sheeps clothing.

A quick comparison: 2004 Z06 has a smaller throttle body-76mm vs. 90 mm for the 2005 C6. The Z06 has a 5.7 liter motor vs. the 6.0 liter LS2. The intake manifold has been redesigned to accommodate the better flow characteristics of the throttle body, and the heads are also improved from a port configuration standpoint. i.e. a ported LS6 head. The compression ratio was automatically increased with the new swept volume from the additional displacement and Z06 combusion chambers to 10.9:1 vs. 10.5:1. Iridium plugs, and hotter coils mean better combustion.

Bigger fuel injectors than the 2004 Z06 with four hole injectors are rated at 4.1 g/s vs the older 3.67 g/s (both at 400 kilopascal or 58 psi rail pressure)

The Z06 heads being utilized flow 15% more air on the intake side, and 21% more on the exhaust port side. 2.00"/1.55" valves are the same steel valves as the LS1. but the springs are Z06.

The exhaust manifolds flow 4% better than the Z06 exhaust manifold (our dyno testing in 2001 suggested that shorty headers vs. the LS6 headers, showed zero improvement in horsepower or torque, so GM has done some homework here) with the straight through mufflers reducing backpressure 10%, and now no pup cats! Finally. No A.I.R. pump! Bay to bay breathing as in the Gen III Z06, has been a part of the LS1 and LS6 for a few years now.

The cam used is the 2001 Z06 cam, with a .525"/.525" lift (2004 Z06 cam is .555"/.551" and similar duration, so here you can subtract 10 RWHP, for the C6 with the same head port design, but with the increase port flow, the actual loss from a lower lift may be insignificant. We have the present Z06 cams, ready to install as soon as our C6 comes in.

They have also gone back to the lower tension rings found in the 2001 Z06, but without the oil consumption problems, which means less frictional losses. Anodized ring lands, may help strengthen the lands, but not from forced induction senarios. I am very disappointed that forged pistons were not used.

GM would have you compare the LS2 to the LS1 to keep the Z06 hot rodders happy, but the truth is out there. The real comparison should be the LS2 vs. the LS6. The LS2 is the new KING of horsepower, no matter how GM spins it.

With all of the above changes to the basic Z06 platform, do they expect anyone to believe that there is only 5 HP LESS than the Z06...???

From a marketing standpoint, it would kill the remaining 2004 Z06 sales, if the new C6 became available with 420 advertised HP.

One more thing. When the Z06 (LS7) motor hits the scene, the 3 valve head design, dry sump, and 427 cid will bump the horsepower to 535. GM will claim much less on paper.

Jim Hall

[Modified by Jim Hall, 7:53 PM 4/29/2004]

At the upscale Detroit Opera House, on January 4, 2004, GM held a snazzy, invitation only event for the unveiling of the brand new C6 Corvette with Rick Wagoner, GM Chairman and CEO, as the main speaker. Perhaps Jim Hall was at this event, or some other information session, learning about what makes Corvette’s new, LS2 engine tick. Jim was obviously well informed, because he was 100% correct with his 420+ horsepower prediction with a caveat. He stated, “…you can subtract 10 RWHP…” for the cam, which results in the same 410+ horsepower that preproduction LS2s rated under the imminent, certified protocol.

Power Progression: LS6 – LS2 – LS3

LS6 heads were originally designed with more than enough air flow to accommodate a 405 horsepower LS6 engine. So, identical LS2 heads (243 castings) already had enough air flow to feed 406 or 407 HP as measured with the original SAE J1349 rating procedures used by all U.S. auto manufacturers from 1972 through 2005. When Chevy rated the preproduction LS2 with what became the new, for model year 2006, SAE certified protocol, it measured between 410 and 415 HP. All GM engines that were rated under both standards had higher horsepower numbers with the new certified protocol.

A redesigned C6 platform allowed for better induction and exhaust air flow than was possible with the C5 platform, including the C5 Z06. LS2’s increased air flow, compression and cubic inches resulted in a stronger engine than the 2002 to 2004, 405-HP LS6.

Two sets of heads were developed for the LS7 engine. The first heads were ultimately rejected because they couldn’t produce the desired power. After some additional work, these heads were used on the LS3. LS3’s fuel injectors and induction system ahead of the throttle body (MAF sensor, air box and duct) also came from the LS7—these parts flowed more fuel and air than necessary, but since they were already inventoried, using them eliminated extra engineering, development, production, and inventory costs. LS3’s throttle body and exhaust system, except for a small change in the manifold to match the head’s reshaped exhaust ports, were from the LS2. Using off-the-shelf parts was a cost effective way to reach 430 SAE certified horsepower in a normally aspirated, overhead valve, 6.2-liter engine.

Horsepower per cubic inch

SAE net (pre-2006)

2001 LS6 – 1.1127 (385/346)
2002 LS6 – 1.1705 (405/346)
2005 LS2 – 1.1154 (406/364)

SAE certified (post-2005)

2005 LS2 – 1.1291 (411/364)
2008 LS3 – 1.1436 (430/376)

Increasing an engine’s cylinder volume will increase torque, however, without corresponding increases in air flow and/or compression, power per cubic-inch will decrease. LS2 and LS3 engines had significant increases in air flow. LS2’s increased compression plus improved intake and exhaust flow were spread over a 5.2% increase in cylinder volume and LS3’s improved heads and cam along with better intake flow were spread over a 3.3% cylinder volume increase. Higher volume increases require correspondingly higher air-flow rates to maintain equal power levels per cubic-inch of total cylinder volume. This explains why LS3’s horsepower per cubic-inch is greater than LS2’s (LS2’s cylinder volume increase was 36.5 % greater than LS3’s) and why the 2002 LS6 had a significant increase in power per cubic-inch over the 2001 LS6 (no change in cylinder volume).

Evaluation of Information Presented and the 395-HP LS2 Dustup

Advertised manual-shift, LS3 performance (12.4 sec. @ 117 mph) was arrived at with a Z51 equipped coupe that included the dual-mode exhaust, 436 horsepower engine. At the 2008 National Corvette Museum Birthday Bash event, Chevrolet's power point presentation stated manual shift performance figures were arrived at with a Z51 optioned car. Base car performance probably was 12.5 seconds @ 116.5 mph.

From conversations with GM personnel at the 2007, National Corvette Museum Birthday Bash event, Corvette Forum member, talon90, stated that “… the best times possible were presented.” The only way to come up with "the best times possible" would be to use cars equipped with Z51 and a rating of 436 hp. This makes good marketing sense, enabling advertising to report a greater differentiation with LS2. LS2 was underrated at 400 horsepower, so by using a performance-optioned car, LS3 power difference looked to be more than it actually was. There was really only a 20 horsepower difference and that is what advertised performance numbers show. Twenty-five horsepower is needed for a 2-mph, quarter-mile speed advantage (436 – 25 = 411) so 20 horsepower is needed for a 1.5-mph advantage for the base LS3 (430 – 20 = 410).

Comparing the performance numbers:


Base manual coupe – 12.6 seconds @ 115 mph (Chevrolet advertised)
Z51 manual coupe – 12.5 seconds @ 115 mph (Chevrolet unadvertised)


Base manual coupe – 12.5 seconds @ 116.5 mph (Estimated)
Z51, NPP manual coupe – 12.4 seconds @ 117 mph (Chevrolet advertised)

GM states there is a .2 second and 2 mph difference in quarter-mile performance between LS2 and LS3 Corvettes rather than the actual .1 second difference between the Z51 equipped cars used in testing. Chevrolet had to use the .2 second time difference because the LS2-Z51 time of 12.5 seconds was never used in general advertising except for Corvette Quarterly magazine, a limited GM publication. Therefore, it was necessary to use the LS2 base car time of 12.6 seconds in performance comparisons with LS3. This is why there is a .2 second, advertised time difference. Quarter-mile speed differences between a LS3 with standard exhaust and one with the NPP option varied little from what was advertised.

It appears that when the LS3 Corvette was first introduced at its 2007 Corvette Museum unveiling, Chevrolet’s PowerPoint presentation purposely omitted showing that Z51 and NPP exhaust optioned cars were used for performance testing. Also, LS3 power was compared to the 395-horsepower, Trailblazer SS LS2. Apparently this was done to make the new model Vette look like a bigger improvement over the previous LS2 car than it actually was. This was a poorly done marketing ploy. The following year’s PowerPoint presentation made a small but significant correction, showing that manual shift performance figures were derived with a Z51 equipped car—the 436 horsepower option was still not mentioned. Surprise!...Finally!...At the April, 2009 National Corvette Museum C5/C6 Bash, Tadge Juechter, Corvette Chief Engineer, said that performance times for LS3-Z51 cars were obtained with the 436 horsepower engine.

Another mistake was made at the 2007 information session: The new LS3 Corvette was given credit for a 7:56 time at Germany’s Nürburgring. That time was actually run by the 2004, C5-Z06 CE Corvette … Chevrolet never ran an LS3 Corvette at the Nordschleife. It was common knowledge that a 2006, LS2 Corvette had already established a time of 7:59 at the “Ring.” Why did Chevy slant their 2007 presentation of the new LS3 Corvette with wrong and misleading information? I believe it was to cover the fact that the LS2 had been underrated—showing a greater performance differentiation would accomplish that.

LS2 should have received a 406 SAE Net horsepower rating when it was first introduced in the new, 2005 C6 Corvette and then a 410 or 411 SAE certified rating in 2006. There were two reasons this did not happen: Chevrolet’s concern about offending C5-Z06 owners by having an equal or more powerful engine in the new base Corvette and a thirty horsepower increase in the upgraded 2008 model sounded more appealing than twenty horsepower.

Beginning in 2006, GM policy was to rate all new engines, as well as existing engines that were continuing in production, to the new SAE J1349 protocol with SAE J2723 certification. Corvette’s LS7 was the first engine to receive a rating under the revised standards. It was initially rated at 500 horsepower under the old J1349 standard, but gained five horsepower under the new. If LS2 had also been given a certified rating, Chevy would have been forced to advertise LS2’s true numbers. I’m sure marketing played a part in the decision not to rerate. The engine was only one year old in 2006, still too close to the 2004 C5-Z06, and being able to advertise a 30-horsepower increase in the C6’s fourth production year (2008) would be a great selling point at just the right time. Also, rerating the LS2 to 410 or 411 Certified horsepower in 2006 would have been a large power increase for an existing 400 horsepower engine, proving that LS2 was intentionally underrated at its introduction in 2005.

It is common knowledge that GM monitors Corvette Forum, providing an easy and low expense method for taking the pulse of Corvette owners. On occasion, company personnel make anonymous comments on the forum if they believe input is needed. For example: A PowerPoint presentation at the 2007 National Corvette Museum Birthday Bash event, showcasing the brand new 2008 Corvette, included information stating that LS2 made 395 horsepower. This caused a stir on the Forum. Eventually Harlan Charles, Corvette product manager (forum name 1990z51), entered the fray by stating, “The engineer I talked to told me the LS2 data was from the Trailblazer SS not the Corvette.” ( Without identifying himself, he attempted to head off a developing storm where forum members began doubting that the Corvette LS2 was a 400 horsepower engine. I talked to Harlan about the 395 HP figure at the 2007 Corvettes at Carlisle show. He again verified that it came from the Trailblazer SS, the only Chevy vehicle still being manufactured with the LS2 engine. Was the 395-HP figure an intentional misrepresentation or was it just a mistake by a lower level employee assigned with the task of putting together the PowerPoint presentation?

There are two GM charts that compare LS2 and LS3 power and torque. The 2007 NCM event chart in question here (, is labeled 2008 "LS2" vs "LS3". It compares a Trailblazer SS, 395-HP, LS2 engine to a 2008 LS3. There is another GM chart that compares a Corvette LS2 (this chart can be seen here in post #1) that is labeled 2007 "LS2" vs. 2008 "LS3". The 2008, Trailblazer SS chart plainly shows a different power curve than the 2007, Corvette LS2 chart. At about 5,000 rpm, the 395-HP LS2 curve levels off and begins to waver rather than continuing a steady, smooth climb to 400 HP as the Corvette LS2 does. Individually or in combination, there is an obvious difference in either the Trailblazer's cam, engine calibration, intake manifold or exhaust system. So to answer my own question: A Corvette LS2 power curve was not used in the PowerPoint chart that labeled the engine as a 2008 LS2. What wasn't said in the presentation is that the only LS2 being used in 2008 was the Trailblazer SS version. GM's presenters omitted a key piece of information by failing to reveal that LS2's power curve was not from a Corvette. I believe this was intentional, because peak-power rpm was changed to 6,000 rather than the 5,400 rpm where Trailblazer's LS2 had previously peaked at 395 horsepower. The RPM change was probably done to disguise the numbers as coming from a Corvette LS2. After the presentation, a number of people asked about the low rating; certain GM personnel answered by saying LS2 was rated under the new certified standard. If GM had planned to officially rerate LS2 under the new SAE protocol, it would have been done for model year 2006, as were all other existing GM engines rated under both standards. GM would not have waited until 2008 to rerate one engine in its last year before cancellation. By 2005, GM had already planned LS2's replacement and consequently never went to the expense of having LS2 officially certified under the new SAE guidelines. For GM, the number 400 was perfect: It didn't violate C5-Z06's exclusivity when the C6 was introduced and it allowed for advertising a 30-horsepower increase for the 2008, mid-model upgrade; so why change it? A 30-HP increase sounds a lot better than 20, especially when sales are dropping because of the subprime mortgage crisis of 2007-2008* and the rising "Great Recession." The answer that LS2's 395-horsepower rating was from the new certified procedure makes no sense and was apparently part of the cover-up.

GM's willingness to juggle numbers for marketing purposes means that a shift in power and torque lines on a chart is not beyond the realm of possibility. LS2 graphs 400 horsepower on GM's comparison chart with LS6; the power curve was probably shifted down from the 405-407 level. Also, at the 2007, NCM PowerPoint presentation, the LS2 horsepower curve may have been changed by the presenters, or their staff, to show Trailblazer SS' peak HP at 6,000 rpm rather than the 5,400 rpm where it actually occurred.

I have no doubts about the accuracy of my conclusions because they were based on information from key GM personnel and people that have direct access to those who design and build the Corvette. Also, my calculations were made from Chevrolet’s performance numbers. As Crush1 stated, “…the base C6 measures, with the new SAE specs, in the range of 410-415 HP.” If Chevrolet had introduced the LS2 in 2006, when the new rating system became available, it would have been rated at the low end of that range. Otherwise, LS2 would have been rated at 410 or 411 SAE Certified horsepower.

*Deteriorating economic conditions affected Corvette sales beginning with the 2008 model year: 2007 LS2 Corvette production was 32,402 cars; 2008 LS3 production was 27,579; 2009 LS3 production fell drastically to 12,080 cars produced. GM tried to stop the decline in sales with the 2009 introduction of the Grand Sport, but low production numbers continued each year until the end of the C6 model run in 2013 with 10,765 LS3s produced. More LS2 Corvettes were produced during three years (2005-2007) with total production of 97,523 cars than LS3s produced over six years (2008-2013) with total production of 72,409 cars.

Supporting posts:

LS2 Power in Australia

From Wikipedia

LS2 engine in a 2005 Chevrolet Corvette

The LS2 was introduced as Corvette's new base engine for the 2005 model year. It produces 400 hp (298 kW) at 6000 rpm and 400 ft·lbf (542 N·m) at 4400 rpm from a slightly larger displacement of 6.0 L (5,967 cc/364.1 CID). It is similar to the high-performance LS6, but with an improved power peak and more torque throughout the rpm range. The LS2s in the E-series HSVs are modified in Australia to produce 412 hp** (307 kW) and 412 ft·lbf** (559 N·m).

E Series all-new Holden Commodore chassis, known as the VE was unveiled in July 2006. Following this, a new range of "E" Series HSV models were released in August 2006.

Changes to the exhaust system yielded a 10 kW (14 PS; 13 hp) increase in power (see below) for the LS2 to 307 kW (417 PS; 412 hp**).

**Power and torque measurements have changed from the stricter ECE method in the Z series to the DIN method for the E series. The use of 98 RON* fuel is also now recommended over 95 RON. Thus the actual power increase is likely to be less than 10 kW (14 PS; 13 hp), however, the exact amount cannot be determined without testing data. DIN horsepower is the power measurement protocol in the German DIN standard 70020. It is sometimes abbreviated as "PS", which stands for Pferdestärke, which is the German word for horsepower. DIN hp is measured at the engine's output shaft, and is often expressed in metric (Pferdestärke) rather than mechanical horsepower.
________________________________________ ____________________

*Australia's 98 RON fuel is equal to fuel that is rated at 93 RON+MON/2 in the United States. The two countries use different methods of rating fuel octane.

The kilowatt (kW) was wikipedia's base unit used to measure engine power. Kilowatts can be converted to SAE net horsepower by dividing the kW unit by .7457. SAE net horsepower, in turn, is converted to DIN (PS) horsepower by multiplying by 1.0139. The E-Series LS2 is rated at 307 kW. Dividing 307 kW by .7457 gives 411.6971 or 412 SAE net horsepower and multiplying 411.6971 times 1.0139 gives 417.41625 or 417 PS (DIN) horsepower. SAE net and DIN are two different methods of measuring engine horsepower, but vary so little in their procedures that they are nearly identical and are easily converted to one another.

Before modifications, the Australian LS2 made 297 kW (404 PS; 398 SAE net) on 95 RON fuel. Corvette’s LS2 makes 303 kW (412 PS; 406 SAE net) on 93 RON+MON/2 fuel, which is the equivalent of Australia’s 98 RON.

Power increase from using 98 rather than 95 RON fuel can be found at this web address: Even though improvements were made to the L76 engine, the 10 kW power increase is the same as the LS2 engine experienced with the same modifications. Quotes from the article:

“Holden says the engine, codenamed L98 is almost identical to the L76 version launched in Commodore late in 2005. The fitment of a dual exhaust system with quad outlets raises peak power 10kW to 270kW and torque 20Nm to 530Nm.

The dual exhaust lowers back pressure by 12 per cent and also increases that trademark burble favored by V8 drivers.

There’s also another catch with fuel; 270kW and 530Nm can only be achieved using more expensive 98-octane unleaded.

Using regular unleaded, power will drop about 7 kW (to 263kW in total) and torque drops 22Nm to 508Nm.”

A 7 kW power increase from using higher octane fuel translates to 9 SAE net horsepower (7/.7457 = 9.387). The Holden LS2 made 398 SAE net horsepower before calibration to use 98 RON fuel and the addition of a performance exhaust increased power to 412 SAE net. That amounts to a 14 horsepower increase, 9 coming from the octane boost, which means the remaining 5 horsepower came from exhaust improvements. Those 5 horsepower closely match the 6 horsepower increase LS3 engines experience with the optional NPP exhaust system. Corvette LS2 engines were rated using 93 octane fuel, the equivalent of Australia’s 98 RON fuel. It seems that the only difference between the Corvette LS2 and its Australian cousin, which is rated at 297 kW (404 PS; 398 SAE net) using 95 RON fuel, is the octane fuel that the engine was rated with. If we add the 9 horsepower gained with higher octane fuel to the 398 rating that Holden gave its LS2 the result is 407 SAE net horsepower. That is a perfect match with what Tony Holloway, Crush1 and what a high level Corvette powertrain engineer stated LS2 rated on GM’s engine dynamometers. Holden then added 5 more horsepower with a better exhaust system. The following quotes describe the better flowing exhaust:

“Engineering and technology

Under the bonnet the unique-to-HSV 6.0 litre LS2 V8 now produces 307kW @ 6000 rpm (up from 297kW @ 6000rpm) and 550Nm @ 4400rpm (from 530Nm @ 4400rpm) thanks to a revised intake and exhaust system (including new smooth flowing 'four-into-two-into-one' tubular extractors) and a 24 month program to refine the engine calibrations, positioning Grange as one of the fastest luxury/sports limousines in the world.”

“Holden says the engine, codenamed L98 is almost identical to the L76 version launched in Commodore late in 2005. The fitment of a dual exhaust system with quad outlets raises peak power 10kW to 270kW and torque 20Nm to 530Nm.”

Holden’s L98 and LS2 engines have a true quad outlet—two on each muffler, but without a dual-mode flap that can be had as Corvette option NPP. The standard Corvette exhaust has a single outlet on each muffler, which then splits into quad tips. Holden’s HSV LS2 has short tube extractors (four-into-two-into-one) rather than the Corvette style (four-into-one) cast iron exhaust manifold. From the quoted information, it is difficult to determine what the exact exhaust difference is between the Holden 297 and 307 kW LS2 engines—what we do know is that there was a 10 kW power increase from using higher octane fuel and exhaust changes. That 10 kW increase is the exact increase experienced by the L76 engine because of higher octane fuel requirements and exhaust improvements. I think it is reasonable to assume that power increases in both engines can be apportioned similarly, meaning that both engines experience an eight or nine horsepower increase from the use of higher octane fuel and a five or six horsepower increase from exhaust changes.

Because Corvette’s LS2 and HSV's 307 kW LS2 were rated using the same octane fuel, Holden’s E-Series exhaust is the reason that the Australian LS2 (412 SAE net hp) makes five or six more horsepower than Corvette’s version (406 SAE net hp), just as Corvette’s NPP exhaust adds six horsepower to the LS3 engine.

Why didn’t Chevy advertise the 405 to 408 SAE net horsepower that the Corvette LS2 actually rated considering that Holden was truthful with their advertised ratings? Answer: Because Chevy was concerned about offending C5-Z06 owners by advertising the true power rating for LS2 and they wanted to show a bigger than warranted power increase for LS3--all the better to sell more Corvettes in the third model year refresh. Holden did not have those concerns because they do not sell Corvettes in Australia.

The following autoblog article calls into question the 412 lb-ft of torque mentioned by wikipedia in the first paragraph, stating that the HSV LS2 makes 412 horsepower and 406 lb-ft of torque: Wikipedia also contradicts the 412 figure, stating that the E-Series LS2 makes 550 N-m or 410 lb-ft of torque at this address:

Kilowatts (kW) is not a method of measuring horsepower, it is a different unit of measure and can be converted to SAE net horsepower by dividing the kW value by 0.7457.

DIN Horsepower – This is a standard, DIN 70020, for measuring horsepower that very closely matches SAE net. The conditions of the test vary slightly, but the required equipment on the engine and the point of measurement (flywheel) remains the same. Because the test conditions are so similar, it is safe to divide DIN horsepower by 1.0139 to arrive at SAE net. This value is so close to equal that for all but the most technical purposes DIN and SAE net are interchangeable.

**Important Notation—Factors .7457 for kilowatts and 1.0139 for DIN horsepower convert to the original SAE J1349 standard for determining SAE net horsepower. These factors do not convert to the revised SAE J1349 with SAE J2723 certification, which was first used to measure horsepower for the 2006 Corvette Z06 LS7 engine. LS7 was initially rated at 500 SAE net horsepower before being rated at 505 SAE Certified horsepower with the new method.

Last edited by Marina Blue; 05-17-2015 at 06:11 PM. Reason: Production numbers added
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Old 09-20-2008, 03:55 PM   #6
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Default LS2 - LS3 Quarter-Mile Performance + LS2 Corvette at the Nürburgring and 190 MPH LS2

Factory Performance Numbers – Manual Shift

Performance Optioned Cars Used in Testing

LS2 Z51 – 12.5 seconds @ 115 mph
LS3 Z51 + NPP – 12.4 seconds @ 117 mph (436 hp)

Difference, Z51-NPP – .1 sec. and 2 mph
(LS2 = 411 Certified Horsepower)

Magazine TestsAll cars tested were manual shift with Z51 performance option

12.6 seconds @ 114 mph (Dec. 2004 Car and Driver)
12.6 seconds @ 113.2 mph (Jan. 2005 Motor Trend)
12.7 seconds @ 113 mph (Sept. 2004 Car and Driver)
12.8 seconds @ 114.5 mph (March 2005 Road & Track)
12.9 seconds @ 112.3 mph (Dec. 2004 Road & Track)

Average - 12.72 seconds @ 113.4 mph

LS3 – Cars tested with 436 hp NPP exhaust option
12.4 seconds @ 117 mph (December 2008 Car and Driver)
12.4 seconds @ 116 mph (September 2007 Car and Driver)
12.5 seconds @ 115 mph (September 2007 Motor Trend)
12.6 seconds @ 115.7 mph (January 2008 Road and Track)
12.8 seconds @ 113.5 mph (September 2007 Road and Track)

Average – 12.54 seconds @ 115.44 mph

Difference - .18 seconds and 2.04 mph

“The List”—Corvette Forum

Red = LS2
Green = LS3

11.71 @ 119.94 - AndrewZPSU - 08 M6 - (2590) #1 (Excluded)
See this thread:
11.8 @ 118.82 - GMrulz - 08 A6 Z51 NPP - (3482) (Questionable factory stock status due to abnormal performance)

Top Seventeen LS2 & LS3

12.10 @ 117.60 - dingrao - 08 A6 - (3565)
12.15 @ 115.59 - Old Goat - 09 A6 2.73 - (3712)
12.16 @ 116.54 - Vinsane112 - 08 A6 2.73 - (2744)
12.17 @ 116.80 - Pettvette - 08 A6 - (3290)
12.18 @ 117.72 - Hardhattg - 08 Z51 M6 - (2690)

12.21 @ 115.45 - LS1LT1 - 06 A6 - (1282)
12.23 @ 115.58 - 06C6FVR - 06 Z51 M6 - (337)

12.23 @ 112.86 - 940CACC - 08 Z51 A6 - (2880)
12.26 @ 115.22 - Oklahoma - 08 A6 - (3767)
12.27 @ 118.66 - EZ28 - 08 Z51 M6 NPP - (3251)
12.31 @ 114.82 - CYA Vett - 05 F55 M6 - (679)
12.35 @ 117.47 - Bain - 08 A6 2.73 npp - (2759)
12.38 @ 115.86 - Proney - 07 M6 - (3521)
12.40 @ 114.70 - Jschindler - 08 Z51 M6 NPP - (2138)
12.41 @ 116.15 - Jtorchz06 - 09 Z51 A6 NPP - (3190)
12.41 @ 115.38 - HOXXOH - 08 A6 F55 - (2486)

12.42 @ 113.90 - DrRichie - 05 Z51 M6
12.49 @ 115.54 - 1.8T - 08 Z51 M6 - (2314)
12.49 @ 114.90 - Jschindler - 05 Z51 M6
12.53 @ 113.00 - Wicked07C6 - 07 Z51 M6 - (918)
12.54 @ 113.59 - Tony 63 Vette - 06 A6 - (1514)
12.54 @ 113.74 - Tony96LT4 - 06 Z51 A6 - (1153)
12.55 @ 114.70 - Larry R - 08 A6 2.73 - (4058)
12.56 @ 113.39 - Red Sleeper - 06 A6
12.56 @ 112.00 - Orange C6 - 05 Z51 A4 - (60)

12.60 @ 114.12 - Beefcake - 08 A6 - (2882)
12.63 @ 114.88 - Prankster - 06 M6 - (1625)
12.65 @ 114.99 - PhillyLS1 - 09 M6 - (3156)
12.65 @ 111.65 - Zippin Zee - 05 Z51 M6 - (51)
12.66 @ 113.61 - CFP40 - 08 A6 2.73 NPP - (2834
12.66 @ 113.03 - Mdrrandall - 07 Z51 M6 - (1649)

12.69 @ 112.32 - Silverlx - 06 A6 - (876)
12.70 @ 112.43 - Jelsis - 06 Z51 A6 - (456)
12.70 @ 113.00 - Blackmajik - 07 A6 - (1631)


LS2 – 12.5176 seconds @ 113.74 mph
LS3 – 12.3553 seconds @ 115.74 mph

Difference – .1623 seconds and 2.00 mph


Of the three sources for Corvette quarter-mile performance statistics, Factory Performance Numbers are the most reliable. Chevrolet’s numbers come from an average of numerous runs made by the company’s professional drivers, with consistently prepared cars, at the same track, under controlled conditions and then adjusted for standard day temperature and barometric pressure. These numbers are the most accurate representation of a Corvette’s performance capabilities and are the only ones that should be used when making a comparison between different models of the car.

The small number of performance tests and varying driving methods used by different magazines as well as inconsistent weather and track conditions, car preparation, and driver skill for entries on Corvette Forum’s “The List” can result in performance numbers that do not match those reported by Chevrolet. Another problem is that factory stock status of entrants on “The List” cannot be verified. The only fair way to compare magazine tests would be to have LS2 and LS3 cars driven on the same day, at the same track, with the same driver using equally prepared cars. “The List” on Corvette Forum will never be a reliable measure of performance differences between LS2 and LS3 because there are too many uncontrollable factors, however, I do find it to be quite a coincidence that the quarter-mile speed difference between LS2 and LS3 matches perfectly with Chevrolet's reported numbers. I suppose the "law-of-averages" is at work here.

Another consideration affecting performance is normal production inconsistencies resulting in a four to six horsepower difference in LSx engines and differing parasitic friction losses within the remaining drivetrain. This can result in up to a .6 mile-per-hour speed variance in the quarter-mile. Chevrolet tries to adhere closely to scientific methods during testing by balancing out power differences between cars. Magazine testers and Corvette owners at the local drag strip are not able to do this.

Chevy’s advertised 2-mph quarter-mile speed difference between LS2 and LS3 is supported by both “The List” and magazine tests regardless of their inherent inconsistencies.

By adding Chevrolet’s own performance figures, the top legitimate manual shift time from “The List” (Hardhattg, 06C6FVR) and all magazine test numbers, the resulting average is:

LS2 – 12.63 seconds @ 113.94 mph
LS3 – 12.47 seconds @ 115.99 mph

The difference is .16 seconds and 2.05 mph.

All three sources of quarter-mile performance numbers, even in combination, support a .1 to .18 second and 2-mph advantage for LS3.

2006 Corvette Z51 at the Nürburgring

According to Dave Hill, Corvette Chief Engineer and Vehicle Line Executive, a manual shift, 2006 Corvette Z51 ran a time of 7-minutes, 59-seconds at the demanding Nürburgring Nordshliefe course in Germany, which is used by manufacturers to performance test their cars. A lap time under 8:00 minutes is considered to be world class and difficult to achieve. Hill stated that the car used in the test was a 2005 model built out to 2006 specifications. A 2005 spec. car did not do under 8:00 minutes. This run was done in very hot and humid weather by Jan Magnussen immediately after the 2005 running of the 24-hours of LeMans race in France. Cooler weather probably would have been conducive to a faster time. This 2006 spec. Corvette came within 3-seconds of the 2004 Corvette Z06 CE time of 7-minutes, 56-seconds. Z06 models from 2001 to 2003 were not able to break the 8-minute barrier until suspension and shock-valve settings were changed and fine tuned for the 2004 model year. Commemorative Edition Z06s had carbon-fiber hoods that weighed 10-pounds less than normal. Dave Hill was extremely proud of how close in performance his base C6 Corvette, with Z51 performance package, was to the top performing C5-Z06 Corvette. The Z06 has nearly a 100-pound weight advantage as well as a better performing wheel/tire combination (wider, non-EMT tires on smaller diameter wheels).

A full lap of the Nordschleife track is 20.832 km (12.944 miles) long. Chevrolet runs the track from a standing start, whereas other manufacturers use a running start. This would result in slightly slower times for Chevrolet. For example: A 2005 Porsche 997 Carrera S using a PASM setting “Performance” also ran the “Ring” in 7:59 with the advantage of a running start and the ability to be choosey about weather. Porsche, as a German manufacturer, has greater access to the Nürburgring track than Chevrolet. Weather, the driver, and using a standing or running start will affect track times. Walter Rohrl, Porsche's company driver, is extremely familiar with the track.

190 MPH With Factory Stock LS2 Corvette

Chevrolet advertises that a LS2-equipped, C6 Corvette can reach a top speed of 186 miles-per-hour (300 KPH). With a few minor adjustments, the 2005 Corvette used to reach 186 also did 190 MPH with Corvette Test Driver Mike Neal at the wheel. Here is the story as reported in the October 2004 issue of Corvette Fever magazine:

Three hundred kilometers per hour is a magic number, sort of like gaining membership to the 200-mph club at Bonneville. When the team drove their production spec C6 to GM’s Arizona Proving Grounds, they knew they should be able to just make it to the 300-kph mark, bragging rights they intended to own.

According to Corvette Test Driver Mike Neal, “We went as a team; we all had to be there.” GM’s 5-mile, Arizona-desert test track is plenty big, but is basically a circle. “We got it up to 184 mph or 298 kph,” said Neal. But driving in a constant corner, he was always scrubbing off speed and they couldn’t get it to the 300-kph mark. The team knew they needed to go someplace with a straight long enough to get to the true top speed. So they rented the high-bank test track now owned by Nissan, just 45 minutes away, knowing it was longer, had 36-degree banking and 1.7-mile straights. They had one day to get the job done.

Brake Engineer Tony Rifici looked on from the pits as Neal came up to speed. “You could see this car going down the straightaway at about 186 mph and it looked like it was parked.” There was almost no lift to the front end.

Neal said, “When I drive at top speed in the C5, you can see the front of the car lift. The steering gets very light and I just say, ‘We’re going to be very careful here.’” He calls it “in full rebound.” But Neal says the C6 feels exceptionally stable and comfortable approaching the upper limits.

Once the car was warmed up and some practice laps taken, it took more than a full lap at the track to get up to speed. Powertrain Integration Engineer Luke Sewell watched from the sidelines as Neal brought it full tilt into the first turn. He noted, “That was the only time I ever heard Mike say, ‘That was pretty scary!’” According to Neal, the middle of the turn is a no-brainer, but approaching the turn, the track goes into a bank first, still in a straight line, then into the turn. “So,” he said, “you have to correct to the left slightly just before you get into the turn, then bring it gently back into the banking.” But it didn’t take long at that point to settle in and take it to 186 mph. The team had their record by running at 300 kph in both directions on the course.

Then, just ahead at 186 mph…

Later in the day after the record was secure the team decided just for fun, to pull in the outside mirrors and add a little duct tape to the car for another run. If you can touch 186 mph; well, you can certainly make 190. Right?

Approaching the almost vertical banking, Neal had it flat out and spotted a roadrunner (a bird, not a Plymouth) coming up the banking. “I’m in the middle of the corner,” said Neal who was totally committed to his line at that point. “Well, I was pointed where he was going.” We all sat on the edge of our seats, knowing you don’t dodge something at that speed. What happened? “Well, did you ever see how smoke looks in wind-tunnel testing?” After all those years, all Wile E. Coyote needed to catch the roadrunner was a C6.

While certainly not happy about hitting anything, Neal stayed the course with his right foot buried. With folded mirrors and duct tape, they hit 190 mph, topped off the tank, and drove it home.

Last edited by Marina Blue; 03-22-2015 at 09:12 AM. Reason: Add 190 MPH With Factory Stock LS2 Corvette
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Old 09-20-2008, 04:06 PM   #7
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Originally Posted by Marina Blue View Post all-time favorite, the 1967 Corvette with L71 engine.
In its "as installed" (SAE NET) configuration, which includes the full factory exhaust system, all engine accessories, the full air cleaner assembly and more realistic atmospheric correction factors, the L71 produced roughly 350 SAE NET HP (virtually identical to a bone stock LS1).

A few of the magazines of the period obtained freakish results that would suggest more, though those "press cars" were factory prepared "ringers" - a common practice of the period.

In it's SAE NET configuration, the "legendary" ZL1 could only muster 376 HP:

The old cylinder heads and chambers were no match for the CAD designed, modern stuff and the understanding of the combustion process itself has matured dramatically since the sixties (and seventies and eighties...)

Summarily, the a bone stock LS2 outguns ANY of the old bone stock 427s.
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Old 09-20-2008, 04:11 PM   #8
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Nice write up. Very informative
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Old 09-20-2008, 04:17 PM   #9
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Default Reasons Why LS2 Should Have Been Rated At 406 Net or 411 Certified Horsepower

Tony Holloway, who has a key position in Corvette powertrain assembly, stated that LS2 engines rate from 406 to 408 SAE Net Horsepower on GM’s engine dynos. The range of these numbers match the power variation in LS7 engines observed by Katech Engineering and the Society of Automotive Engineers (505 to 508 hp) showing both engines are manufactured to the same tolerances of variation in production.
*Refer to “Conversation With Tony Holloway” Manuscript (Post 2)

Corvette Forum member, Crush1, stated, “I have been told by someone in Chevy, that I cannot quote, that the base C6 measures, with the new SAE specs, in the range of 410-415 hp. Prior to the revised specs it measured in the 405-408 range (as reported in other posts in this thread) so for the 2005 models they rated it conservatively at 400 hp. If the base C6 had not been released until 2006, it would have been rated higher. I suspect for marketing reasons they chose to leave the rated HP alone for 2006.”

When comparing Chevrolet’s performance numbers for LS2, LS3 and LS6 engines, reliable sources and calculations tell us that the LS2 should have received a SAE Net rating of 406 horsepower under the original SAE J1349 specifications and 411 SAE certified horsepower under the latest SAE J1349 procedures. This is reasonable considering all GM engines rated under the previous SAE J1349 standard and then under the newer certified standard gained from 1 to 29 horsepower—the Corvette Z06 LS7 engine gained 5 and the Cadillac STS-v gained 29 horsepower under the new standard. LS2 never received an official certified rating from GM.
*Refer to “Corvette Quarter-Mile Factory Performance Specs” Manuscript (Post 3)
*Refer to “The effect of horsepower and weight on quarter-mile trap speeds for C6 Corvettes” Manuscript (Post 4)

Corvette Forum member Jim Schindler (jschindler) has often reported that his 2005 manual shift Z51 coupe would stay even with a 405 horsepower Z06 when racing was done from a rolling start. He often ran against two friends that owned C5 Z06s modified with headers, cold air intake, and aftermarket tuning resulting in chassis dyno ratings of over 380 horsepower. Jim’s friends were amazed at how close his stock LS2 stayed to their modified Z06s. This is fantastic performance for a 400 horsepower LS2 considering that the C5 Z06 is lighter in weight and has smaller diameter 18” wheels with non-runflat tires weighing less than C6’s 19” wheels with run-flat tires. One would suspect that LS2 has a few more ponies than its advertised 400.

Corvette Forum member TTRotary owned both a C5 Z06 and a LS2 equipped C6 Corvette. He stated, “When I bought the C6, I was pretty sure it was noticeably slower than my Z. Since I still had it, I got a friend to drive and we did some highway pulls from 45 or so. To my surprise, the C6 was right there with the Z through 120. It was interesting, the C6 would pull on the Z at the low end of each gear and the Z06 would catch it back on the top end of the gear. The C6 was Z51 so same gearset. As an experiment, we swapped rear wheels. The Z could no longer pull. So I'd conclude that the 6.0L is a pretty stout motor if it can move a heavier car that well despite have same HP. Also, the C6 tune, as you know, is a dog. After Shawn's tune, my LS2 has that same razor-sharp response the LS6 had.” Considering that both Corvettes had the same gearing, it becomes obvious that LS2 must have power at least equal to LS6’s 405 horsepower in order to be competitive with the lighter weight Z06.

There have been numerous claims that the 405 horsepower C5-Z06 makes a few more horsepower on a chassis dyno than the LS2. This is most likely the result of increased inertia created by the greater rotating mass of larger diameter wheels and heavier run-flat tires on C6 cars and the effects of knock-retard engine management on the higher-compression LS2. In fact TTRotary reported that his C6-LS2 rated 360 horsepower on a chassis dyno and that his Z06-LS6 rated 355 horsepower on the same dyno under nearly identical conditions. So much for his LS2 not being as powerful as his LS6.

Chassis dynamometers seem to show that there is approximately a 35 rear-wheel-horsepower difference between manual shift LS2 and NPP exhaust equipped LS3 cars. Some of this difference can be accounted for by changes in the LS3 drivetrain: a new TR-6060 manual transmission; peak power occurring at a lower RPM; a new type of differential gear oil with better lubricating properties; a lighter weight forged wheel option, all of which result in less power lost to friction or inertia. Also, full-throttle, 4th-gear pulls on a chassis dyno result in varying degrees of knock-retard spark control depending on conditions during the run. LS2 engines are more susceptible to damaging detonation under full-throttle because of their slightly higher compression ratio and LS3's better combustion quality; making LS2 more affected by engine-saving, feedback-spark-retard than LS3. I believe the use of 95-octane fuel would eliminate most intrusions of spark control and therefore reduce the amount of RWHP variance we're seeing between dynos and cars. The fact that chassis dynos are notably unreliable predictors of actual flywheel horsepower is a result of the numerous variable factors that need tending to get an accurate reading, which makes comparisons between chassis dynos, or even different cars measured on the same dyno, a difficult task.
*Refer to “LS2 – 400+ Horsepower?” Manuscript (Post 5)

Hot Rod Magazine tested a LS2 crate engine at Katech Engineering producing 400 horsepower on Katech’s engine dyno. But Jason at Katech stated that “The exhaust configuration on the engine dyno is different than what is in the car, the controller is different, and there may also be other variables.” This means that Hot Rod’s test did not result in numbers equal to what GM would see through corporate testing. Also, there are variations of the LS2. GM Performance Parts Catalog shows LS2 crate engine cam specs that are not as aggressive as Corvette LS2 cam specs, creating another uncertainty. If the printed figures are correct, crate engines have less power than Corvette installed LS2s. Hot Rod’s test cannot be compared to GM factory test results.

In a Corvette Forum thread titled “C6-Z51 vs C5-Z06 Comparo Provides Insight on Torque Management Impact,” John Armstrong (Ranger) compared spreadsheet statistics of the fastest recorded quarter-mile times for a factory-stock, 405-HP, C5-Z06 (J-Rod) and factory-stock, manual-shift, C6-Z51 (06C6FVR). As Ranger points out: “It compares the quarter-mile splits and incremental times of two very well driven Corvettes in very similar weather (DA) and at the same fine track (Houston Raceway Park). Passes were at the same time of year, mid-January, a period of very favorable race conditions there.” At the eighth mile the LS2 is trapping 91.18 mph compared to LS6’s 95.29 mph, a 4.1 mph deficit. Ranger points out the impact of torque management (knock-retard, feedback spark timing?) at launch and with each shift for the C6 and that torque management is non-existent in the Z06. An interesting thing happens by the end of the quarter-mile; LS2, pulling a heavier car and driver—Daren (06C6FVR) weighs 260 pounds—with larger diameter and heavier wheels, has narrowed that deficit to only 1.3 mph with a final speed of 115.58 mph compared to the LS6’s 116.9 mph. Over that last 660 ft. the Z51 gained 24.4 mph compared to the Z06 gaining 21.61 mph. This clearly shows that the LS2, unhindered by torque-management/feedback-spark-control in that last eighth-mile, is stronger than the 405 horsepower Z06. Considering the Z06’s advantage in weight and wheels along with being unrestricted by torque-management/feedback-spark-control and running in a slightly better DA, this chart proves that LS2 is the more powerful engine and is making at least 405 original SAE J1349 Net horsepower.

Last edited by Marina Blue; 05-19-2015 at 06:44 PM. Reason: add: . . . "knock retard" timing tables . . .
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Old 09-20-2008, 04:28 PM   #10
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Originally Posted by 05vettelag View Post
Nice write up. Very informative
The "old school" people go nuts about these things. They reference urban legend rather than facts.

Here's a good reference to the facts behind the ZL1 "legend." Contrary to what seems to be "popular opinion," ZL1 cars didn't have a prayer of running with a new, bone stock C6 unless the ZL1's were fitted with open long tubes and various other mods.

I have the referenced R&T Duntov test; the car actually weighed 2,908 pounds and was utterly gutted.

The second car was also gutted and fitted with 4.88 gears and various other GM "skunkworks" mods. I would suspect milled heads and perhaps some porting on that one...

"Chevrolet enthusiasts still living in the bygone musclecar era might argue the 1969 Corvette with the ZL1, all-aluminum, 427 was the quickest production example ever built. Unfortunately, most performance numbers for ZL1s are urban legend that came out of a media preview held at the GM Milford Proving Ground a generation ago.

In the summer of 1968, the press sampled two special, ’69 ZL1s. The first was a partially-gutted, 3000lb, white convertible fitted with the optional hardtop and set up by Chief Engineer, the late Zora Duntov, himself with road racing suspension, open headers and race tires–hardly production trim. It ran the quarter in 12.1 at 115mph. The second was red coupe built for drag racing by development engineer Gib Hufstader (who today, though semi-retired, still consults to GM Racing) with a 4.88:1 rear end, open headers, a race-prepared Turbo-Hydramatic 400 automatic and 9-in. slicks–again, hardly production equipment. That car usually ran low 11s and dipped into the 10.9s at 132mph when launched with a neutral start."
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Old 09-20-2008, 04:39 PM   #11
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Default L-71 & L-72 True Gross & Net Horsepower

As harddrivin1le mentions, the LS2 also outguns L-71. I previously wrote about this topic as a possible magazine article. I didn't use it, so I'll post it here. Please excuse my 427 - 454 table--I couldn't get it to line up so this is the best I can do.

L-71 & L-72 True Gross & Net Horsepower

Early 1966 L-72 427 engines were rated 450 horsepower at 6400 rpm. Not long after production began, these engines were given a lower rating of 425 horsepower at 5600 rpm. The lower rated engine had no changes from the one that had previously been 450 horsepower. Chevrolet’s central office apparently realized that a 450 hp rating would attract the attention of safety minded politicians and insurance companies thereby forcing the reduction. Also, there seemed to be an unwritten agreement between Ford, Chrysler and GM that no engine would be rated over 425 hp no matter how powerful it was. In 1967, Chevy broke that rule by rating the L-71 (triple 2-barrel carb, solid lifter, 427 cu. in.) engine at 435 horsepower. L-71 was identical to the 1966 L-72 except for the intake system. L-72 had one 4-barrel carburetor compared to L-71’s tri-power set-up.

Over the years there has been much speculation about the actual horsepower output of these two engines. Some people believed the L-71 made nearly 500 gross horsepower. However, performance and dynamometer numbers tell a different story. All known magazine quarter-mile times for L-71 and L-72 equipped Corvettes averaged 13.38 seconds at 107.94 miles-per-hour. For equal weight cars, quarter-mile trap speeds are an excellent indicator of horsepower. Magazine tested LS1 equipped C5 Corvettes had the same trap speeds as L-71 and L-72 Corvettes. (See Addendum) Because big-block C2 Corvettes are nearly the same weight as a C5, we can assume they equal the 345 to 350 SAE net horsepower that LS1 engines make.

Corvette Fever magazine had an article titled “Big-Block Power Tune” in their November 2006 issue where a correctly restored 1966 L-72 Corvette was meticulously dyno tuned in order to determine horsepower gain from the tune. Here are the numbers they came up with: Before dyno tune – 289 rwhp @ 5000 rpm and 331 lb.-ft. torque @ 3800 rpm; After dyno tune – 301 rwhp @ 5000 rpm and 342 lb.-ft. torque @ 3800 rpm. This car was restored showroom original for acceptable street operation and was equipped with the more restrictive “N14 Side Mount Exhaust System”. A standard under car exhaust would most likely have resulted in somewhat higher numbers and probably at a higher rpm. Maximum horsepower was reached at 5000 rather than closer to 6400 rpm where an open exhaust would have produced peak power. On average, the 345 net horsepower LS1 engine also produces 300 rear-wheel-horsepower (rwhp). Equal rwhp for both the LS1 and L-72 translates to 345 net horsepower for the L-72.

For the 1970 model year, Chevrolet developed 454 cubic-inch engines to replace the 427. Listed here are the 427s with their 454 replacements and power ratings:

427/ 454 equivalent
L-36, 390 hp/ LS-5, 390 hp
L-68, 400 hp/ LJ-1, 400 hp*
L-72, 425 or 450 hp/ LS-6, 450 hp
L-71, 435 hp/ LJ-2, 460 hp
L-88, 430 hp/ LS-7, 465 hp
ZL-1, 430 hp/ LT-2, 465 hp

With preparation for their introduction well under way, all 454 engines except the LS-5 and LS-6 were cancelled due to GM’s de-proliferation program to eliminate costly options as well as high insurance rates and top management’s desire to tone down horsepower. Eliminating the Corvette engines (LJ-1, LJ-2, LS-7, LT-2) from production was untimely as it was too late to put LS-6 on the Corvette option list. These cancellations left Corvette in the unusual position of having less power than the 1970 SS454 Chevelle, for which LS-6 remained an option. Chevrolet corrected this the following year by making a lower compression, 425 horsepower version of the LS-6 an option for the 1971 Corvette, but deleted it from the Chevelle’s option list.

To prepare customers for the 1972 switchover from a gross to net method of rating horsepower, Chevrolet reported both gross and net ratings for 1971 Corvette engines. The Corvette LS-6 received a 425 gross and 325 net horsepower rating. The gross to net conversion factor for that engine was .7647 (325/425) which can be used to convert our previously determined 345 net horsepower for L-72 to a gross rating. Using that factor we come up with a gross rating of 451 horsepower (345/.7647 = 451.16) for the L-72, which for all practical purposes is exactly the same rating Chevy initially gave the engine.

The 1970 SS454 Chevelle, with a 454 cu. in., solid lifter, high compression, LS-6 engine was rated 450 gross horsepower at 5600 rpm and 500 lb.-ft. torque at 3600 rpm. That engine had the same internals (camshaft, heads, lifters, etc.) and 780 cfm carb as the L-72 427. Many enthusiasts thought LS-6 was the more powerful engine, but Tom Langdon, a 1960’s Corvette powertrain development engineer had this to say, “Increasing the stroke without enlarging the bore doesn’t translate into a real increase in power. Some of that extra power is eaten up by increased friction. A good 427 (L-88) would put out about 600 horsepower. The 454 pulled more torque, but power was just about the same as the L-88.” (Classic Corvette – The First 30 Years by Mike Mueller, 2003 by Crestline ISBN 0-7603-1806-9 first published by MBI Pub. Co. 1994, page 322) Langdon’s statement also applies to the L-72 and LS-6. They were identical engines except for stroke derived cubic inches and both made 450 horsepower. (I wish I could verify the source, but somewhere I did see that a correctly restored 1970 SS454 Chevelle made the same chassis dyno 300 rwhp as the previously mentioned 1966 L-72 Corvette.)

Notice that the 425 horsepower L-72 and 450 horsepower LS-6 are both rated at 5,600 rpm. This had to be a carefully considered rpm number for Chevrolet. If the LS-6’s 450 horsepower had been advertised closer to 6400 rpm, where peak power actually occurred, the new 454 would have looked no stronger than the 427. It was not a secret that early production L-72s had been rated 450 hp at 6400 rpm. The 454 did develop more torque, but torque doesn’t sell fast cars—horsepower does. Chevy had to make their new engine look more powerful than the old one and 5,600 rpm accomplished that.

With the introduction of the 454 engine, Chevy gave us more realistic horsepower ratings. It was becoming all too obvious the high-performance era was near an end and that the horsepower wars were drawing to a close. With nothing to lose, this may have prompted more accurate reporting. LS-6 was given a believable 450 horsepower rating and LJ-2 (L-71’s triple-carb 454 replacement) was slated for 460 horsepower. However, truth in ratings did not extend to LS-7 and LT-2—the 454 replacements for L-88 and ZL-1. Both should have been rated at over 500 horsepower rather than the scheduled 465. Chevy wanted to be honest, but not that honest. There would have been some explaining to do if the horsepower prohibition watchdogs realized street going rocket ships were being sold and powered by L-88 and ZL-1 engines.

True gross horsepower numbers for the L-88 were established in 1992 by Corvette Fever. An engine dyno test of a correctly restored 1969 version of the L-88 cranked out 513 lb.-ft. of torque at 4200 rpm and 514 horsepower at 6200 rpm. Engine dyno tests were also performed on a factory equivalent ZL-1 and reported by the The Camaro Research Group ( Their web site states the following: “Although rated at 430 horsepower by the old method, Chevrolet never released actual power figures for the as-installed production ZL-1 engine. Numbers were tossed around for years until Bill Porterfield decided to find out. Bill had acquired an original block from one of the COPO Camaro cars and enough NOS parts to complete another engine. The engine was subjected to 5 levels of testing. RPM was limited to 6750 rpm.” This engine developed 523.6 horsepower on the fifth test with all accessories removed, open headers, the carburetor re-jetted and timing set to 39 degrees BTDC. These L-88 and ZL-1 dyno numbers may seem low to some, but they match perfectly with a statement made by Tom Langdon— “525 horsepower was no problem for a ZL-1 right out of the crate. With some attention to detail to the cylinder heads, etc., producing up to 600 horsepower was within reason.” (Classic Corvette – The First 30 Years by Mike Mueller, 2003 by Crestline ISBN 0-7603-1806-9 first published by MBI Pub. Co. 1994, page 317) Unfortunately there were no known similar tests of as delivered from the factory L-72 or L-71 engines.

We have determined that the L-72 engine had a true rating of 450 SAE Gross and 345 SAE Net horsepower. Now let’s look at the L-71. The only difference between the two engines was carburetion. L-72 had one Holley 4-barrel flowing 780 cfm and L-71 had three Holley 2-barrel carburetors capable of feeding the engine at 1,000 cfm. This triple carb set-up gave the L-71 an official rating of 435 hp @ 5800 rpm. Along with flowing more air, tri-power provided a more efficient flow to the cylinders, all of which resulted in ten more horsepower. However, that 435 rating was not the peak horsepower L-71 actually produced. It most likely made the same 460 SAE Gross horsepower that LJ-2 was to be rated at and 352 SAE Net horsepower (460 x .7647). Langdon’s statement that a 454 developed more torque but the same horsepower as an equivalent 427 is the basis for assuming that L-71 and LJ-2 made equal power. A 460 horsepower L-71 makes perfect sense. We have already established that L-72 made 450 gross hp and Chevrolet maintained a ten horsepower difference between tri-power and 4-barrel equipped 427 and 454 engines.

Even though L-71 received a higher power rating, actual performance between L-71 and L-72 is very close. In fact L-72 had the best magazine quarter-mile time, albeit not by much (L-71 = 12.9 sec. @ 111 mph vs. L-72 = 12.8 sec. @ 112 mph). The L-72’s 4-barrel carburetor may give it a slight quarter-mile performance advantage. Some drag racers claim that a 4-barrel provides better power delivery than a triple carb set-up. Tri-power L-71s operate on the primary center carburetor until you put your foot into it, then the two secondary carburetors, controlled by a mass-air vacuum signal from the center carb’s venturi, open up for full power. Those progressive, vacuum controlled secondary carbs may be a slight disadvantage in the quarter-mile, but when working properly make for a smooth build-up of power. If driven conservatively, L-71’s primary center 2-barrel provides better gas mileage than the 4-barrel equipped L-72.

Magazine performance numbers and chassis dyno figures mixed in with a little Corvette history make a compelling argument that Chevrolet did have their horsepower ratings correct for early production L-72s and the LS-6, but in-between, advertised L-72 and L-71 ratings were on the low side. Factory delivered horsepower numbers for both these engines are equivalent to the 345 and 350 net horsepower rated LS1 engines, but with the installation of headers and a less restrictive exhaust, power increases dramatically.

L-72 – 450 SAE Gross HP, 345 SAE Net HP
L-71 – 460 SAE Gross HP, 352 SAE Net HP

Note: I found the following period 426 Hemi dyno test, which supports my conclusion of a 460 horsepower rating for L-71. A 426 Chrysler Street Hemi is close enough in power to a solid-lifter, Chevy big-block to be used as an approximation of what kind of power is realistic for L-71. A 426 Hemi showing 463 corrected horsepower is apparently not a race engine, but one that was intended for street use as was the L-71. The 3 horsepower difference between this Hemi and a 460 HP rated L-71 is of no concern. Advertised ratings usually are not exact for an individual engine, but at the low end of normal production variances for the group of tested engines.

426 Hemi Dyno Test—Chrysler Corp. dyno test, July 9, 1965

Quote: Straight from Chrysler Corporation! We'd love to publicly thank the person who sent this, but must keep his name confidential...not that we know his real name! Note the maximum horsepower on this dyno run - 433.5 hp (that's 463 corrected horsepower!), 405 lb-ft of torque at 6,000 rpm. Max torque was a whopping 472 lb-ft at 4,000 rpm with 336 lbs of load (also max load; corrected). So when did it reach 425 horsepower, its rated level? If you use the corrected figures, it had passed 425 horses at 5,200 rpm!

It should be noted that this is not necessarily a test from a production engine. Our source wrote: "the dyno tests were conducted in cells 12 and 13 of Building 135 in the old Highland Park complex." The test sheets were found nearby, apparently discarded.

*It is assumed LJ-1 was the 454 replacement for the 427 tri-power, 400 horsepower L-68. This is logical because a 1970 Corvette assembly manual shows a 400 hp LJ-1 engine getting the same M40A hydra-matic transmission as the 390 hp LS-5, thereby classifying both on the lower performance end of hydraulic lifter big-block engines. Looking at RPO codes for 454 engines, it becomes obvious the slot for LJ-1 is right after LS-5 (refer to listing in paragraph four). Mike Mueller, in his book Classic Corvette – The First 30 Years, mentions the possibility that LJ-2 was the 454 equivalent of the 427 L-89 engine, which would make LJ-1 the 454 equivalent of L-71. However, I don’t think this is a likely scenario because aluminum heads were not a popular option and the trend at GM was to get rid of costly low production options. All considerations point to LJ-1 as the 454-replacement engine for L-68 and LJ-2 as the equivalent of L-71. I believe Mueller agrees with this as he refers to LJ-2 as the tri-carb L-71 replacement various times with the possibility of an L-89/LJ-2 connection only once.


Magazine Quarter-Mile Times for L71 and L72 Corvettes

12.8 sec. @ 112 mph (1966 L72, Nov. 1965 Car and Driver)
12.9 sec. @ 111 mph (1967 L71, May 1967 Cars, Martyn Schorr)
13.3 sec. @ 108 mph (1968 L71, May 1968 Hi-Performance Cars)
13.4 sec. @ 109 mph (1968 L71, Oct. 2007, Corvette Fever, Ranger)
13.4 sec. @ 105 mph (1966 L72, March 1966 Motor Trend, McVay)
13.41 sec. @ 109.5 mph (1968 L71, June 1968 Car and Driver)
13.6 sec. @ 105 mph (1967 L89/L71, 1967 Car and Driver)
13.8 sec. @ 108 mph (1967 L71, May 1967 Hot Rod, Eric Dahlquist)
13.8 sec. @ 104 mph (1967 L71, April 1967 Motor Trend)


13.38 sec. @ 107.94 mph

Magazine Quarter-Mile Times for LS1 Corvettes

13.0 sec. @ 109.6 mph (2003 LS1 350 hp Convertible, 2003 Motor Trend)
13.2 sec. @ 109.3 mph (1999 LS1 345 hp Coupe, May 1998 Motor Trend)
13.3 sec. @ 108.6 mph (1999 LS1 345 hp Hardtop, September 1998 Motor Trend)
13.3 sec. @ 106.8 mph (1997 LS1 345 hp Coupe, February 1997 Motor Trend)
13.4 sec. @ 105.5 mph (2000 LS1 345 hp Convertible, February 2000 Motor Trend)


13.24 sec. @ 107.96

I only had access to LS1 performance numbers from Motor Trend magazine. However, Motor Trend usually shows better performance results than other magazines except for Car & Driver. I believe additional tests from Road & Track and Automobile would lower the average. I also suspect using numbers from an equal number of 350 hp cars would raise the mph average somewhat, but I believe the end result would be about the same as what I have calculated here.

Average performance results show identical quarter-mile speeds for LS1 (107.96 mph) and L-71 plus L-72 Corvettes (107.94 mph).

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Old 09-20-2008, 04:48 PM   #12
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The problem with the old tests is that many of the cars weren't really stock. Factory "ringers" were common back then. I tend to ignore the data from that era that is clearly well outside of the norm (e.g. the '66 "Car and Driver" 427 'Vette that was in fact a "pre-production car" that almost certainly wasn't representative of final production car performance).

Check out the last page of this article, which was written by Ro Mcgonegal 25 years or so after he originally tested/wrote about the "stock" 440-6 pack for "Super Stock" magazine:

Here's a good one on the "stock" 1964 GTO that ran 0 - 60 MPH in 4.6 seconds and turned the quarter in 13.1. People quoted those times as gospel for decades until the truth finally came out:

Here's one from HOT ROD that was written back in the eighties:

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Old 09-20-2008, 04:51 PM   #13
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Nice write-up.
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Old 09-20-2008, 05:00 PM   #14
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Originally Posted by danl72 View Post
Nice write-up.
The real farce with the old stuff can be found in the "pure stock" drags. Those cars LOOK production like stock and the series' name suggest they are.

A closer look into the rules reveals the truth: Overbores, "improved stock" cams, forged aftermarket rods/cranks/pistons, milled heads, fully locked diffs, any axle ratio, valvetrain work, 3 angle valve jobs, modern, 2.5" dual exhaust systems, etc.

One guy is running twelves in a "certified stock" 1970 350 Cutlass. "Certified stock" has somewhat stricter rules, but his car is still roughly 2 seconds and 10 MPH quicker than how it first left the factory in 1970.

The engines in those series can be modded to NHRA tech specs. In some cases, milling the heads and decking the block to those specs can gain nearly 3 full points in actual compression. (They all run high octane racing fuel in that series.)
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Old 09-20-2008, 05:35 PM   #15
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Old 09-20-2008, 05:53 PM   #16
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That sounds like some good solid research! Do you want to write my dissertation?
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Old 09-20-2008, 06:13 PM   #17
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wow....I think I'll just take your word for it.
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Old 09-20-2008, 06:22 PM   #18
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So all this for 7 more bhp I've for one never cared, my LS2 makes 450rwhp SAE as it is now, stock heads (cai, FAST, cam, etc). However, props to you, very nice write-up and good information. Good comparison between the LS3 and LS2 1/4 mile runs Should make this a sticky up top.
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Old 09-20-2008, 06:36 PM   #19
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Originally Posted by Daytona Bob View Post
I couldn't have said it better!
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Old 09-20-2008, 07:26 PM   #20
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Default Lots of back up info.

Great write up. Your fingers must be tired, from typing. -- -- Your forum name indicates the mid 60's.

Last edited by mcwire; 09-20-2008 at 07:28 PM. Reason: forum name
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