LT1 vs LT4 pros and cons?
Thread Starter
Burning Brakes
Joined: Oct 2019
Posts: 1,110
Likes: 119
From: USA
Le Mans Master
Joined: Aug 2015
Posts: 6,102
Likes: 1,981
From: St. Charles MO
Right, at the crank. These are net numbers, so they include losses to engine-driven accessories, full filtered intake and exhaust - IOW, the engine as it is actually installed in the car. In the old days they basically ran them with no accessories, open headers, unrestricted intake, etc. That's the difference between SAE net (now) and gross (old days). Net is more accurate for the car's power as purchased. But in either case, it's always at the crank.
Thread Starter
Burning Brakes
Joined: Oct 2019
Posts: 1,110
Likes: 119
From: USA
Right, at the crank. These are net numbers, so they include losses to engine-driven accessories, full filtered intake and exhaust - IOW, the engine as it is actually installed in the car. In the old days they basically ran them with no accessories, open headers, unrestricted intake, etc. That's the difference between SAE net (now) and gross (old days). Net is more accurate for the car's power as purchased. But in either case, it's always at the crank.
for example the 1970 400sbc was 265hp gross and in 72 it was 170hp. thats nearly 100hp loss from ac pump, alternator and air cleaner. makes no sense
Last edited by Garack; Nov 14, 2019 at 11:18 AM.
Melting Slicks
Joined: Jun 2011
Posts: 2,383
Likes: 385
From: Leland , North Carolina
I find this subject a bit confusing. Excluding California, I see people from time to time saying their 85 or 89 didn't pass emissions. What is the general rule on early c4s? Does it just vary from state to state on visual vs tailpipe emissions?
Last edited by TommyFox; Nov 14, 2019 at 11:21 AM.
Safety Car
Joined: Aug 2000
Posts: 4,148
Likes: 642
From: Bandera Texas
I had my smog license for 28 years in California. Every two years, the car must go thru a visual test where all factory emission gear is on a car 1977, YES 1977 .....and newer, and then go thru a dyno test with the sniffer up the tail pipe to measure HC and CO, and NOX readings. If items are missing and / or readings are exceeded, it is a ''no pass''......
New York, Mass, and Maricopa Cty, Arizona have similar laws. And more states are implementing new laws to raise money and clean the air.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
You need to take a moment, and carefully READ THIS THREAD about how HP is measured.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
As you'll see and read in my linked thread above, GROSS hp was with everything removed. Everything. They may have retained the water pump back in the day, but that would be it. It was typically an attempt to get the best possible number that a long block (and intake) could produce. NET HP is defined as the "power available to move the car", at the engine. So that power is measured (at the crank) with every parasitic draw being accounted for.
Finally, I'd bet that from '70-'72 the 400 lost compression and cam for emissions purposes and likely added an air pump.
EDIT: Bingo...
1970 400 2 bbl 9.0-1 compression 265 hp 400 ft lbs tq @2400 rpm (this would be GROSS rating)
1972 400 4 bbl 8.5:1 compression 170 hp @3400 rpm 325 ft lbs of torque @2000 rpm (this would be NET rating)
.
Last edited by Tom400CFI; Nov 14, 2019 at 01:17 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Le Mans Master
Joined: Aug 2015
Posts: 6,102
Likes: 1,981
From: St. Charles MO
- Visual test: are all the emissions components still on the car and do they appear to be in operative condition?
- Tailpipe sniffer test: measures the actual emissions as the car runs on a dyno.
- OBD2 Scanned emissions: connects a state-monitored scanner to the car's diagnostic port and pulls all info that is stored on the ECM about the car's current and past emissions performance.
Every state is different, and some vary from county to county. Where I live, 96-up vehicles (i.e., all cars with OBD2) have to pass the scan test. I guess they may have to pass visual too, although my experience is that they aren't looking too hard or don't know what to look for.
Thread Starter
Burning Brakes
Joined: Oct 2019
Posts: 1,110
Likes: 119
From: USA
It does make sense...because it's more than just the ac pump, alternator and air cleaner. It's full exhaust, EPA cert'ed tune, hot running temps, power steering pump, cooling fan, water pump....
As you'll see and read in my linked thread above, GROSS hp was with everything removed. Everything. They may have retained the water pump back in the day, but that would be it. It was typically an attempt to get the best possible number that a long block (and intake) could produce. NET HP is defined as the "power available to move the car", at the engine. So that power is measured (at the crank) with every parasitic draw being accounted for.
Finally, I'd bet that from '70-'72 the 400 lost compression and cam for emissions purposes and likely added an air pump.
EDIT: Bingo...
1970 400 2 bbl 9.0-1 compression 265 hp 400 ft lbs tq @2400 rpm (this would be GROSS rating)
1972 400 4 bbl 8.5:1 compression 170 hp @3400 rpm 325 ft lbs of torque @2000 rpm (this would be NET rating)
.
As you'll see and read in my linked thread above, GROSS hp was with everything removed. Everything. They may have retained the water pump back in the day, but that would be it. It was typically an attempt to get the best possible number that a long block (and intake) could produce. NET HP is defined as the "power available to move the car", at the engine. So that power is measured (at the crank) with every parasitic draw being accounted for.
Finally, I'd bet that from '70-'72 the 400 lost compression and cam for emissions purposes and likely added an air pump.
EDIT: Bingo...
1970 400 2 bbl 9.0-1 compression 265 hp 400 ft lbs tq @2400 rpm (this would be GROSS rating)
1972 400 4 bbl 8.5:1 compression 170 hp @3400 rpm 325 ft lbs of torque @2000 rpm (this would be NET rating)
.
Last edited by Garack; Nov 14, 2019 at 02:09 PM.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Well...that was all covered in the thread that I posted for you, above. Did you read it?
Basically, there are way too many variables to make a "claim". Why?
Look at a "350" CID example, the C5: No, No smog pump, good, dual exhaust, serpentine accessory drive, large efficient cold air intake.
Now anther 350, a late 70's Caprice: smog pump, single bead style cat, single exhaust, crappy manifolds, small, hot air intake, large cooling fan, 20 V belts....you get the idea.
Hard to compare, but here is an excerpt from the thread I linked above:
Basically, there are way too many variables to make a "claim". Why?
Look at a "350" CID example, the C5: No, No smog pump, good, dual exhaust, serpentine accessory drive, large efficient cold air intake.
Now anther 350, a late 70's Caprice: smog pump, single bead style cat, single exhaust, crappy manifolds, small, hot air intake, large cooling fan, 20 V belts....you get the idea.
Hard to compare, but here is an excerpt from the thread I linked above:
One of the links I posted showed a real world spread from RWHP to Gross with the '70 Chevelle sporting a 383...
"For a baseline vehicle, we used Project Homewrecker, a '72 Corvette with a 383. We thought it perfect for the job since we had engine dyno numbers similar to gross measurements, but had yet to test it on a chassis dyno. The stroker is backed by an M22 four-speed and the IRS contains 3.70:1 gears. On an engine dyno with open headers, no accessories, and the same 750 cfm double pumper carb, it put out 425.8 hp and 473.8 lb-ft of torque. On Super Chevy's brand-new, state-of-the-art Dynojet (www.dynojet.com), it made 283 hp at 5,000 rpm and 341 lb-ft of torque at 3,900 (SAE net correction). That's with everything hooked up-alternator, power steering pump and Vintage Air A/C compressor. Eye opening, isn't it?"
So that is a ~34% loss from Gross to wheel, in THAT car, or turned around, it would be a 50% gain in "hp number" from wheel to Gross. So there is a percentage you could use, but keep in mind that will never be rock solid accurate; many factors come into play, such as:
*How much is done to maximize hp in the "gross" dyno pulls
*drive train weight
*gearing
*transmission type
*Exhaust system....
...and then there were a plethora of other cars in the same article that compared Gross to rear wheel.
HERE IS ANOTHER ARTICLE where Super Chevy took an LG4 from a 3rd gen. LG4 was rated at 145hp NET and on SuperChevy's engine dyno, it did 224hp, GROSS.
"Since it was missing the factory induction system, we simply installed a suitable cast-iron Q-jet intake and carburetor (from the Carb Shop) along with a set of 13/4-inch long-tube headers.... Run with an electric water pump (no accessories), long-tube headers and 37 degrees of total timing, the LG4 produced 224 hp and 308 lb-ft of torque."
-No mention as to how much tuning Super Chev did to it on the dyno...I'd guess that if one were motivated, they could get that number up over 240 with the right fuel and tuning, etc. So now we're looking at over a 36% loss from Gross to NET....and since an LG4 should do about 130 to the wheel...yikes, now we're looking at a whopping 43% loss in "numbers" from GROSS to wheel.
"For a baseline vehicle, we used Project Homewrecker, a '72 Corvette with a 383. We thought it perfect for the job since we had engine dyno numbers similar to gross measurements, but had yet to test it on a chassis dyno. The stroker is backed by an M22 four-speed and the IRS contains 3.70:1 gears. On an engine dyno with open headers, no accessories, and the same 750 cfm double pumper carb, it put out 425.8 hp and 473.8 lb-ft of torque. On Super Chevy's brand-new, state-of-the-art Dynojet (www.dynojet.com), it made 283 hp at 5,000 rpm and 341 lb-ft of torque at 3,900 (SAE net correction). That's with everything hooked up-alternator, power steering pump and Vintage Air A/C compressor. Eye opening, isn't it?"
So that is a ~34% loss from Gross to wheel, in THAT car, or turned around, it would be a 50% gain in "hp number" from wheel to Gross. So there is a percentage you could use, but keep in mind that will never be rock solid accurate; many factors come into play, such as:
*How much is done to maximize hp in the "gross" dyno pulls
*drive train weight
*gearing
*transmission type
*Exhaust system....
...and then there were a plethora of other cars in the same article that compared Gross to rear wheel.
HERE IS ANOTHER ARTICLE where Super Chevy took an LG4 from a 3rd gen. LG4 was rated at 145hp NET and on SuperChevy's engine dyno, it did 224hp, GROSS.
"Since it was missing the factory induction system, we simply installed a suitable cast-iron Q-jet intake and carburetor (from the Carb Shop) along with a set of 13/4-inch long-tube headers.... Run with an electric water pump (no accessories), long-tube headers and 37 degrees of total timing, the LG4 produced 224 hp and 308 lb-ft of torque."
-No mention as to how much tuning Super Chev did to it on the dyno...I'd guess that if one were motivated, they could get that number up over 240 with the right fuel and tuning, etc. So now we're looking at over a 36% loss from Gross to NET....and since an LG4 should do about 130 to the wheel...yikes, now we're looking at a whopping 43% loss in "numbers" from GROSS to wheel.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
In that same thread, there were articles linked. One was comparing a '90's LT1 with a '70 LT-1. Both made 350 GROSS hp. My LT1 made 279 RWHP. So in that comparison, that is a numerical spread of "70" from the LT1's GROSS measurement, to my wheel measurement. It would or could be radically different on a different vehicle, however.
Melting Slicks
Joined: Aug 2018
Posts: 3,127
Likes: 86
Because the LS did not come in a C4 its hard to compare. In the f body the LT1 had more SOTP bottom end driving multiple cars back to back when the were both in the warranty period. The 97 LT4 SLP cars are rare and featured reworked LT4's they ran 13.3. 1/4 mile. 98 LS1 camaro 13.6 1/4 mile
Melting Slicks
Joined: Aug 2018
Posts: 3,127
Likes: 86
No that is not right at all.
You need to take a moment, and carefully READ THIS THREAD about how HP is measured.
You need to take a moment, and carefully READ THIS THREAD about how HP is measured.
Race Director
Joined: Oct 2011
Posts: 16,089
Likes: 819
From: Dallas Texas
2025 C4 of the Year Finalist - Modified
Reworked? Haha. If you rework the LS like they did the LT4’s they will easily blow that time away. Just one turbo on an LS engine would destroy that time slip. LS engines are still king when it comes to horsepower. My 98 Z will stomp my two low mileage C4 cars. All three are completely stock. My wife’s GMC Yukon Denali XL comes close to beating my C4 cars. The 6.2 LS engine is a beast of a motor. I am a former racer so I know how to drive a car and all we do is a straight line shot and she can get het beast moving. Crazy how awesome the LS platform is. LT1/4 are good engines but an LS they are not.
Le Mans Master
Joined: Aug 2015
Posts: 6,102
Likes: 1,981
From: St. Charles MO
Reworked? Haha. If you rework the LS like they did the LT4’s they will easily blow that time away. Just one turbo on an LS engine would destroy that time slip. LS engines are still king when it comes to horsepower. My 98 Z will stomp my two low mileage C4 cars. All three are completely stock. My wife’s GMC Yukon Denali XL comes close to beating my C4 cars. The 6.2 LS engine is a beast of a motor. I am a former racer so I know how to drive a car and all we do is a straight line shot and she can get het beast moving. Crazy how awesome the LS platform is. LT1/4 are good engines but an LS they are not.
Race Director
Joined: May 2006
Posts: 10,691
Likes: 71
From: Phoenix Arizona
Thread Starter
Burning Brakes
Joined: Oct 2019
Posts: 1,110
Likes: 119
From: USA