WydGlydJim

I've always sort of jokingly said the '90s are the quickest........well real world numbers don't lie.

http://www.corvetteactioncenter.com/tech/perform.html

By Corvette Development Engineer, Jim Ingle, GM Proving Grounds
This article first appeared in the November/December 1995 issue of the ZR-1 Registry's, "Legend" magazine and is an excellent, in-depth look at how Corvette performance numbers are established. Jim Ingle is no stranger to the Corvette community. In the 1990s, Jim worked primarily as a Corvette Development Engineer at the General Motors Proving Ground. Among numerous other duties for Corvette and other GM platforms, he is probably most known for his planning/mapping of the Corvette ZR-1 introduction to the automotive press in Carcassone, France as well as several of the long test drives of the early C5 prototypes as described in James Schefter's book, "All Corvettes Are Red". He has also made numerous appearances at the Black Hills Corvette Classic in South Dakota over the years.

Jim Ingle was kind enough to share with us his methods of testing Corvette performance and the results he obtained for Corvette ZR-1s, including the 1989 prototypes. The information he provides here is both interesting and very informative and we would like to thank him for taking the time to share his work with us. He writes:


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This is another discussion best illustrated with torque curves, but I'll try without. First off I should tell you that I run all of the "official" acceleration tests for the Corvette group. Secondly, when I'm testing a car, it's at production specs. (production full tread tires, recommended tire pressure, equipment and I weigh 238 lbs). So, allowing for no equipment, a light driver and minimum fuel, my times are conservative. Our Milford and Mesa Proving Grounds are both near 1000 ft. elevation (sea level times will be quicker); I correct all my times to 60 degrees F (cooler times will be quicker). Reported results are the average of 4 runs: 2 northbound and 2 southbound and are the best in typically 12-16 runs needed to optimize launch (cold or hot tires, launch RPM and shift RPM).

The ideal launch speed is not that which induces minimum wheelspin, but one that maximizes rate of acceleration at vehicle speeds in 1st gear where the no-tire-slip speed puts the engine below its torque peak. In other words, spinning the tires provides much of the same effect that a torque converter does for automatics that don't produce tire spin (typically 900-1200 RPM with the current LT1 engine).

In the case of the LT5 engine, optimum launch is usually a fine line between minimum spin and a "bog" and too much spin resulting in spinning the engine up to the rev limiter. In fact, I've had to use my "Camaro" launch technique on some ZR-1s, where I set RPM and slowly roll in the throttle as the tires hook up. Obviously, the results of this are wildly variable from run to run!

Ok, so what do they turn under these conditions? Here's a list of the 1/4 mile E.T.s (Best, Worst and Average) of the unmodified ZR-1s I've tested each model year:

Year Number Test Weight Best Worst Average Launch RPM Shift RPM
1989 8 3451 12.84 13.05 12.92 2741 6400
1990 6 3493 12.91 13.10 13.02 2450 6300
1991 1 3513 00.00 00.00 13.02 2925 6300
1992 3 3520 13.13 13.23 13.18 2817 6300
1993 8 3513 12.98 13.14 13.03 2430 6716
1994 3 3488 13.05 13.18 13.13 2408 6750
1995 1 3495 12.97 -- 12.97 2450 6875

Causes of the year-to-year variation include changes in weight, emissions rules and tires. The weight increase in 1990 resulted from changes in crash requirements. We had to add a center pole catcher to the front of the car. It not only increased the weight, but it also moved the center of gravity forward and thus the launch traction decreased.

Incidentally, the weight distribution effect on standing-start acceleration is dramatic. I know it sounds like starting the obvious, but I have run tests to measure the effects and the results were surprising.

I ran a weight distribution test on 6 September, 1989 with a 1989 ZR-1 prototype. The baseline curb weight was 3469 lbs. and it ran the 1/4 mile at 13.05 @ 110.7 mph and 0-30 mph at 1.92 sec. (not one of the better '89 prototypes!). I added 300 lbs to the car: 1) under the headlights 2) in the passenger seat and 3) in the rear of the storage area. Here are the results:

Test Weight Distribution 1/4 Mile 0-30 mph
+300 lbs. in front (57.4% of total curb wt.): 13.30 sec. @ 109.8 mph 2.04 sec.
+300 lbs. in center (53.9% front): 13.23 sec. @ 108.9 mph 1.98 sec.
+300 lbs. in rear (46.9% front): 13.14 sec. @ 108.6 mph 1.85 sec.


You'll probably note the mismatch of 1/4 mile speeds with the rest of the results. I didn't do anything to verify this, but I suspect it results from better aerodynamics with the front end closer to the ground. Bottom line: about 0.15 seconds between condition 1 and 3, but a world of difference in the behavior.

One further note: On our test tracks, with little rubber buildup at my launch locations, the tires usually "like" to be warmed up when the temperature is under 60-70 F. However, they like to be cold at higher temperatures.

James Ingle
Corvette Development Engineer
General Motors Proving Ground

8388

Looks like 93' was the best.

WydGlydJim

How so?
'90= 12.91/13.10/13.02 < '93= 12.98/13.14/13.03

ZO6R1

I like the 93 best.....seats, style, and performance.....

Graybeard ZR1

I've never seen him test a car, but "Jingles" is legendary for his ability to put these cars through their paces.
One of his favorite routines for the automotive press was a "durability test" Put it in reverse, back up a bit, wind it up to 7K and dump the clutch in first.
The dude had a great gig.

Sargevette

89 = 12.84

glass slipper

He lost me in the first sentence. He doesn't strike me as much of an engineer if he thinks the torque curve "best illustrates" anything...a very foolish statement. HP is the key and his shift points clearly indicate he left plenty of HP on the table, WTF! Useless info as far as I'm concerned, and yes he short-shifted the '90-'92 cars the worst.

WydGlydJim

I would caution anyone who thinks they now more about how to put a car through it's paces than Mr. Jingles.
Just sayin.

glass slipper

I never said I knew more than Jim Ingles when it came to putting a car through it's paces, you might want to improve your comprehension skills before cautioning anyone. I don't even know him but what he says speaks volumes and while it's possible he may have misspoke, actions speak louder than words as demonstated by his 6300 RPM shift point...what idiot shifts an LT5 at 6300 RPM.

If you think he's so great, please explain how the torque curve illustrates anything better than the HP curve. While you're at it, explain why shifting an LT5 at 6300 RPM is better than shifting at 7000 RPM. Excuse me if your "hero" doesn't impress me.

ZR WON

what idiot shifts an LT5 at 6300 RPM.


In my experience, it's the 'idiot' who wants to run in the 12s with a bone stock 90-92 ZR-1... I've owned mine since 1998, and ran it down the strip more times than most on here. I was stuck on 13.3s@108 *forever* until I read that *exact* article referenced above (I got all the Legend magazines with the purchase of the car). I started shifting at an indicated 6300, per Jingles recommendation, and the 13.0s@110 slips started coming, with a best of 12.89@111.

Bottom line, the LT5 starts losing power very quickly after about 6K RPM with the stock exhaust. The problem is, there are so few *truly* stock ZR-1s out there anymore, I believe people sometimes forget while LT5s may have a *redline* of 7K, they really are just 'making noise' after about 6200. I am referencing 90-92 375hp cars *only*, as that's the version I own. They re-degreed the cams in the 405hp motors for more top end power, and you can see Jingles adjusted his shift points on the later model cars accordingly.

Brian A.
90 ZR-1
12.09@118
01 Z06
not quite stock

Graybeard ZR1

Any 230 lb. driver that can put a BONE STOCK 90-91 in the twelves gets respect. I sure couldn't (@175lbs.).

MY 91" ZR-1 - Bone stock best = 13.15 @108mph. 2.10 60ft.

Same car, N/A stock engine, numerous boltons = 12.06@117mph. 1.76 60ft.

BTW, these times were done while shifting at indicated 7K+.

WydGlydJim

It seemed on the few times I went to the track when I ran to redline the times were worse......the car revs, but acceleration falls off. I just didn't have that much experience with it, so did not want to share.....seems that this is the right way to go......"short shift." Jim is not my hero, but someone who I admire, a geniune good guy, and now that I have more real world experience to back up the article, I'm sure he is right on the money about his shifting points.
Glass slipper my comprehension is fine, you said he doesn't "strike you as much of an engineer." You are an engineer according to your profile, this statement infers you think you know more about things than he does. Then you infer he is "foolish" by one statement, instead of looking at all of the experience, and data collected. Hours and hours of trial and error is not "useless" data. Then in your last post, you all but called a well respected member of the Corvette team ( who you readily admit you don't even know) an idiot. Rather than question someone's comprehension skillls, pay more attention to what you write, and the meaning and context it can be taken in........your just lucky you own a Quasar Blue Z or this would get really ugly!

Vette Daddy

What about the 88's?

MightyZR-1

Here are numbers for my 90 ZR-1 when in stock form in 1993:
80 degrees
Dial-in .000
Reaction time .831
ET 12.721@111.38

Next run

Dial-in .000
Reaction time .670
ET 12.877@113.06

mike100

Was the LT5 one of those engines that had a wide spread of power depending on if you got a good engine or a bad one? Perhaps there are issues with fuel quality and ign timing...

anyhow, I remember racing (statute of limitations should apply on this one) my dad's stock 91 ZR from a roll with my street-strip 12 second Camaro which did 12.90's to 13.10's on normal street radials at 110 mph. pulled hard in first gear and jumped a car out. The vette could stay with the back of my Camaro from then on out, but it was clearly a low 13 second car unless one went through a lot of trouble to get a good dig.

bb62

Based on the numbers shown, the 95 (a 405HP ZR-1) comes out the best with the best average (forget 89 since it never happened). And the 40 pounds penalty the 95 has is nothing. Further, because the 95 had inferior tires to the 90, any current test (because tires would be equalized) would should a increased variance in favor of the 95. Why are the 405 guys not going to like the results (spoken as one who owns a 95)?

NITROUS JUNKIE

Maybe he left the valet key at home

JetJock

I've met Jim Ingles on several occassions at the NCM and talking to the other guys like Jim Minneker, John Heinricy, Dave McLellan and other GM engineers type, Jingles is the MAN when it comes to speed and Corvettes. He is a very unassuming man but he could put a car through the paces and wring out the very best of a car and show you how to drive it. Chervrolet goes by what he said and did. If the numbers he put up there was what he got, then GM took it as gospel.

Bear in mind, he drove these cars before the public even knew about them and he had access to these cars for years before anyone else had them, so I believe whatever he said. He helped redesign the cars because his job was to break them and then help come up with a fix.

WydGlydJim

Since the '95 had only one run, it's best, average, and worst are the same number, and the '90 has a quicker best, so it is quicker.

glass slipper

Here are a few dyno graphs for you.
http://forums.corvetteforum.com/1549544450-post5.html

and another:



The first is from a stock '91 ZR-1 and the second is from my stock '93 ZR-1. While the '91 goes out to 7000 RPM, mine stops at 6750 RPM but the curve can easily be extrapolated to 7000 RPM where it would be over 330 RWHP but we'll just call it 330 RWHP to be conservative. All analysis will be done based on HP because torque is meaningless when it comes to acceleration. When you look at formulas for ¼ mile ET and MPH predictions, the two variables used are weight and HP...torque is not used because it's a force. HP is the rate at which the engine does work and is the proper term to use when accelerating a car to achieve the best time. You always shift at a point where the HP after the shift equals the hp after the shift which usually corresponds to redline but not always.

Looking at the first dyno curve that peaks at ~5700 RPM and ~330 RWHP, HP at 7000 RPM is ~295 RWHP so any shift that results in less HP (~4750 RPM is ~295 RWHP) is considered a short shift (unless you've gone to 7000 RPM) and will hurt your times. The 1st-2nd shift at 6300 RPM and ~315 RWHP leaves you at ~4230 RPM (6300/2.68*1.80=4231) where he has ~255 RWHP while a shift at 7000 RPM leaves you at ~4700 RPM where he has ~285 RWHP. So while J. Ingles short shifts at 6300 RPM to get 255 RWHP to continue his run, I go to 7000 RPM where I still have 295 RWHP. To put it in better perspective, while he goes from 4230-4700 RPM with 255-285 RWHP, I go from 6300-7000 RPM with 315-295 RWHP and only drop to 285 RWHP after my shift. I maintained an average of 305 RWHP to his 270 RWHP...who do you think is going to win that one??? If you continue the same analysis, the 2nd-3rd shift should occur at ~6800 RPM, the 3rd-4th shift should occur at ~6500 RPM, and the 4th-5th shift should occur at ~6600 RPM. If you could pull 6th (let's say some 4.56 gears are in the rear), the 5th-6th shift should occur at 7000 RPM. While I think the numbers on this dyno graph are low in the upper RPMs (because his HP peaked at 5700 RPM rather than the advertised 6000 RPM), I think it still proves my point. A '90-'92 LT5 making HP as advertised would likely have all shifts at 7000 RPM. The exhaust was only ~10 HP difference and the cam timing wasn't changed a significant amount. Cam duration/lift remained the same and in fact, intake timing was left exactly the same and that is what has the biggest impact on how much and where an engine makes HP.

Now look at my curve where HP peaks at ~6200 RPM and ~350 RWHP. With 330 RWHP at 7000 RPM, any shift less than 330 RWHP/5300 RPM is a short shift (unless you've gone to 7000 RPM). Doing the same analysis reveals the 3rd-4th shift at 6900 RPM is the only shift I should make before 7000 RPM...6700 RPM shifts are clearly leaving HP on the table and my real world results confirm that.

Your comprehension skills definitely need some work as nowhere did I compare my driving skills to J. Ingle...please don't put words in my mouth. My post was not even a comment on J. Ingles driving skills. It was a comment on his "engineering" skills if anything. I know plenty of engineers that don't understand the concept of HP and insist on looking at torque. I can accept that from a non-engineer and calmly explain the two concepts in terms a layperson can understand...it drives me crazy to see an engineer that supposedly has the schooling and still doesn't get it. That's probably the emotion you're seeing come through in my posts. He may be a great driver, I don't know and I never made a comment on that. But when it comes to this one particular car, he is an idiot if he was really shifting at 6300/6700 RPM on the '90-'92/'93-'95 ZR-1s...he left a lot of HP on the table and could have gone faster.

If you can come up with a good explanation as to why we should look at torque and not HP as well as a good explanation as to why we should short shift these beasts, I'd love to have that discussion with you or J. Ingle for that matter. I was a member of the "old" ZR-1 Registry and even have the issue you referenced with the article in it.


I've been racing my ZR-1 since new (18 years now) and blindly followed his advice in the article as it was known in the ZR-1 community before it was published. I then did my own analysis and discovered the facts disputed his statements...I stopped short shifting and the closer I get to the rev limiter, the faster I go. It's also why the best/cheapest mod you can do is to raise the rev limiter. This all goes counter to what J. Ingle says in the article...facts and experience!

PS No reason for this to get ugly, it's just a simple discussion among brothers and we can always agree to disagree.