QCVette

Thanks for posting the graphs. I like looking at data like that.

86C4Z51

I love the smell of hot tires when I pull into the garage at home after a spirited drive to the store for wifey.

And I found some old tapes in the back (after having stored the car 4 years). Something about 1980s Zappa music that makes me want to burn rubber.

Paul Workman

So do I. But, too there's an old axiom in statistics one needs not to loose sight of: "The MEAN results do not necessarily apply to the individual." Which...always brings into questions of how the data was collected and under what conditions were the devices under test subjected to, etc, etc.

Note: I'm using LT5 data (because I have lots of it) only as an example illustrating the dangers in drawing hard and fast conclusions about "devices under test", as it were, even or especially from data plotted on a graph.

For example: here is an the LT5's torque and calculated horsepower for a pair of "identical" LT5s, except one is stock and the other has headers. The plot data clearly shows the advantage and disadvantage of those headers (in this case).



Towit:

Does the graph below misrepresent the truth?: Maybe not intentionally...but(!) cutting the throttle off at ≈ 6300 rpm (seen in both graphs - above and below) is a classic mistake many dyno operators make when testing the (DOHC) LT5; often we see graphs cutting off at ≈ 6200 to 6300 rpm - which I think is force of habit (gained from testing so many pushrod motors); almost 1000 rpm short of the LT5's cut-off! Just sayin...

To my point about averages vs. individual results, let's compare results of the two graphs...



Not only was the LT5 cut off way early (bottom graph), but look at that wiggle in the torque/hp graphs prevalent at the high end in two if not all three motor datum as compared to the individual data for the LT5: we don't see the same wiggle in the individual dyno (top) graph - which begs the question, why? (or at least there is some ambiguity afoot).

I guess the point I'm trying to make[/I] is what statistics profs say (with regard to Tom's L98 vs. LT1 data), In order to be valid, independent tests must always faithfully agree when identical tests are duplicated. I have the same graphs in my file that Tom is using to make his arguments, AND several more too supporting his arguments regarding the differences between the stock L98 and the stock LT1. So, IMO, there is little "% of ambiguity" in his arguments, over all (as statisticians might say).

Note: I might add to Tom's argument: The torque advantage of the LT1 above ≈ 3800 rpm is even MORE significant considering it will stay in a lower gear for almost 2000 rpm above the L98 (the word for that phenomenon is horsepower...which cannot be denied!).

I too love analyzing such data and the debates it generates. Valid sample sizes gleaned in like circumstances can dispel myths and 'shine light into the darkness of ignorance'; darkness where the mushrooms flourish on the therein!

Tom400CFI

Great posts w/great info and data!

I can't believe the LT5 picked up ~40 hp from headers alone. I know that wasn't the point of the graph.....but wow.

mike100

It is because it (the headers) actually allows the peak hp to occur at a significantly higher rpm. The stock hp graph on the LT5 is suspiciously flat after peak hp- like it refuses to drop off quickly. Part of that is because of the 4 valves per cylinder design, but the other part is because they are so corked up in stock trim that it just cant go any higher breathing through restrictive intake and exhaust- but it clearly hasn't blown through its useable powerband. Or I guess you could say the LT5 is a 6500+ rpm power peak engine that got corked up

mike100

going back to Lt1 engines. I find them torquey off idle and easy to drive because of that. but also at the same time have enough rev to get going pretty good in the 3rd and 4th gear for a decent top end pull. Kind of outclassed by more modern engines, but pleasant to drive in an intangible sort of way.

Tom400CFI

Well said. I agree w/all of that...especially the highlighted part.

Paul Workman

Having 90% of max torque from just off idle to near red line (read: FLAT), meant its manners in traffic is excellent! (Felt less need to always be down-shifting to scoot when the need to do so arrived unexpectedly!)

MavsAK

From the research I've done, it seems like the LT-5 was even more choked down than the L98 was. Really does make you wonder, what GM could and SHOULD have had, if they had let Lotus do their thing instead of meddling constantly. 500 horses would have easily been in the realm of possibility...and I suspect had that been the case we'd have never heard of the Dodge Viper, after it's first couple of years.

The Northstar suffered from the same culture issues at GM. (weeny displacement, conservative cam profiles, crappy exhaust manifolds, on an otherwise for its time expensive vehicle) probably to make the Pushrod look better. It's a shame GM never realized there is infact room for both.

As for the L98, in autoX it has more effective power to use. Combined, with a marginally lighter weight (which I still say is offset by the granny rubber on the car, and also is thrown out entirely anyway due to the fact that the 88 to 91 cars are also heavier thanks to the chassis reinforcements, and have the same aspect ratio tires, which just leaves suspension setup which is still softer in the 88-91s than the earlier C4s...and yet the car is still faster in autox than the LT-1s), and stiffer suspension to let it USE that higher power in autox rpm ranges, that is why it beats the LT-1 cars so hard. It has more power, -at the same speed ranges that you'd be running-. The LT-1 can't use a "lower gear" because it'll be in first or second most of the time anyway. The power plant, has a 20lb ft advantage, which at that rpm range is vastly more important than the 55hp difference. More power in the same rpm ranges, is more power, and thus more rapid acceleration. Especially if you can keep it to the ground without spinning the tires too much to effect your time.

Tom400CFI

Mavs, your actual auto-x experience oozes from your posts.

Dad3Sons

Hi Guys - I'm late to the discussion, but here goes...

I bought a 96 coupe in March 2014 from a Forum member in SoCal. My first Corvette at age 57. I did a lot of homework on what year/model/engine etc. I chose the 92-96 year bracket because the price point, LT1 engine system and fuel economy/reliability, air bag system, etc. I couldn't be happier with the car. It really didn't need anything thanks to the TLC from the prior owner, but I've been chipping away at some minor items. To really restore it, it needs seats and carpets (SoCal sun damage). But mechanically it's solid. I fixed the dreaded AC Programmer vacuum problem common to the 96 models, so now I have perfect AC on demand through the front vents. You can find a good C4 in the market for around $10K, and be really happy with the car. Just realize it will be a 20+ year old car. I have no regrets! The car is bullet-proof reliable, parts are plentiful of you need them, it's really fun to drive, and it still turns heads and starts conversations. And, keep up with the forums -- a treasure trove of good info!!!

MavsAK

Just like yours where you think 55lbs or less is going to dramatically effect laptimes, with a serious tire, wheel, and brake improvement, to the later car...and it still comes up short vs the old one lighter one

Sorry but tire matters a hell of a lot more than 55lbs or less (using the extreme example.) weight.

The early L98s are gimped if they're on stock wheels compared to the later cars. Especially the earliest cars with their weeny brakes!

The advantage has to be coming from somewhere...

And maybe it's that it's a sum of all of it's parts.

Tom400CFI

I don't believe that I ever mentioned "55lbs". I mentioned, "weight, suspension, etc" -or something like that.



There ya go. Now you're thinking.

You should TRY auto-x some time though...before you say things such as:
beats the LT-1 cars so hard
and
LT-1 can't use a "lower gear" because it'll be in first or second most of the time anyway.

...picking just two examples that really show that you've not done it...or aren't experienced at it (and that's O.K. -just don't tell us 'how it's done when ya don't know).

I've never lost to a TPI C4 in my region w/my car...but do you see me chest-thumping about the "mighty LT1, it's massive low end tq and high RPM hp"? No. You don't b/c I know that the engine has nothing to do with my results. SCCA is not a race of HP (or tq). Honda Civics and Mazda Miatas are evidence of that. If you did it you'd know that.

crowz

Well now I have seen people buy lt1 cars and sell them to go back to an l98 to be competitive. This was back when I autocrossed. These were the same drivers and same cars. Their times were worse on the same course with the lt1's. Also I have personally out done lt1's with my l98 but that's splitting hairs since one person is going to drive better than the other in the same situation.

The l98's in the day when I ran every weekend were flat out turning in better times than the lt1's on slow layout track days. Now there were times we had a good bit of long stretches. On those days the lt1's did better than the l98 drivers.

This was always the discussion of the day at those event and it was a constant ongoing thing on the forum here back then. The consensus we came to was the l98 produced more low end torque than the lt1's.

Im sure some searching on the site here would find those threads unless something has happened to them.

86C4Z51

Either way, it's always fun to drive. Never lose sight of that.

Tom400CFI

I don't doubt or dispute that for a second. I agree that in general, the earlier cars seem to produce better results in auto=x than the later cars.


There is error in that "scientific method", though. The error, is that the engine is not the sole difference between early cars and late cars. There are a plethora of differences that come into play, and most are more important than the engine. You can't determine tq and hp from auto-x results. That is folly. If it worked, then we'd all have to agree that Civics, Neons, and Miatas must be the biggest tork monsters of all tork monsters...right? B/c they will hand it to a Corvette at Auto0-x. How much "low end torque" do Civics Miatas and Neons have though? Not much. Maybe 100 lb-ft?

Can you see how arguing that a 10-20 lb-ft difference at one RPM (reversed, 800 RPM higher) is the reason for "TPI dominance" when cars with 100's of lb-ft less are competitive if not superior? It's a nonsensical position to take.

Auto -x is not a race of hp or tq. it is about handling, average corner speeds, and above all, smooth driving with good lines. Motor has nothing, and I mean NOTHING to do w/those elements. I'm sure you recognize that, since you've done it.

Story time: My first auto-x car was an '83 Trans Am, which started off w/a 305, then later a 350, and after that a 400/T5/3.45. I was always competitive in F-stock and ESP with that car...but rarely won. What held me back? Lots of things, but the biggest break through I had was learning that I had too much tq! Too much. I "fixed" that problem by running events in 3rd gear. First event I did that in, I got FTD and first place. Why? High average corner speeds, and SMOOTH driving. I took away all the herky-jerky on/off tq, engine braking and ***-happiness of the car, and just drove smooth, round lines, with lower tq and smooth power delivery. If auto-x were a race of tq, using second gear would have produced better results....i'd have more tq to the wheel in 2nd. What kind of racing rewards torque? Drag racing.

I agree with 86C4Z51; they're all fun, each w/it's own character.

crowz

I could go with using the civic/Miata line except we were comparing apples to apples kind of since it was vette vs vette generation just different engines basically.

Tom400CFI

Yea, I know they're totally different cars. I agree that it's going off on a tangent and it's apples to oranges...it was just to illustrate how unimportant hp and tq are and especially "low end torque", in autox.

vl5150

I don't care for front drivers like the Honda, I think Miata's are excellent.
As far as pure flogging goes, the Miata is up there with the best and it's a real elemental sports car. The Miata and the corvette are both derived originally from the British sports car. The C1 Vette from the Jaguar and the Miata from the original Lotus Elan. The Vette has long since veered off into something more American ( larger, more powerful, more advanced, heavier), and the Miata stayed a bit more true to the British (lightweight, small, less power, spartan).

But that brings up a good point..

That's really part of the true story of the C4 Corvette. It's the idealized American version of a Jaguar E-Type with a few bits of other inspiration thrown in including earlier vette gens. And that's not a bad thing.

86C4Z51

The E-type, eh? Well if that's the case, I guess there are worse things you could mold your sports car after. Just not build it like the Brits do.

Historically, the best-looking cars (in my ever-so-humble opinion, and in no particular order) are Italian, British and American. The Germans are solid, but spartan (a few exceptions prove that "rule"). The Japanese copied everyone else (they were late-comers), especially with the Miata copying Lotus, Jag, anyone they could think of. And Toyota bragging in the 70s they'd built more twin cam engines than anyone else (like they invented them), while over in Italy, Fiat had been cranking them out for a generation. Meh.

The other nationalities are too small in numbers for my broad-stroke opinion. Holdens and Seats, various French cars etc come to mind.

And all of those countries have also produced hideously ugly cars as well. It's just my opinion, formed over years of watching these things unfold. Not trying to stir up anyone's angst.

I've driven and/or owned and/or worked as a mechanic on all of those nationalities. I'm very happy with America's premier sports car in my garage, with that satisfying American V8 under the hood.