How were C4s so quick
 

I understand compared to now they’re pretty slow or maybe average but the thing is these things from 85-89 made like 240hp? I also recently found out the corvettes weighed quite a bit like 3200 pounds it confused me how these pulled mid 5s in the 0-60 range.

Horsepower isn't measurable, it is calculated based on torque. L98's had plenty of torque, 345 with only 245HP. It is simply because they were low revving engines. When I went from a l98 to an LT1 I was getting better 1/4 mile times but it took the while track to catch up to my buddies in L98 cars. I think the L98 is a GREAT street engine. The LT4 is when GM finally got the power right where torque was high across the page AND they can Rev high to make more HP.

This is also why diesels don't make much HP. My truck has nearly 1000 torque, but hp is in the 400's.

I want to clarify the response above because it may be confusing the issue. HP produced under the RPM band where the engine is used determines how much work can be done or how fast the car will be, not torque.

(Torque x RPM)/5252 = HP

The higher the HP under the band where the car is used will give the most acceleration (Torque by itself means nothing) HP tells you how much work can be done. An L98 makes it HP from 2500 to 4500 RPM (Which means it does have good torque in that same RPM band) but the average HP in that RPM band determines how well the car will accelerate.

the cars certainly lacked power in all regards back in the day. yet they still performed much better than expected.

look at the car minus the power train. chassis was light years ahead of its time, the car is low, somewhat narrow & shaped like a door stop, the engine sits low and behind the front tire, it has a factory 5 link rear suspension, very short driveshaft... is any of this clearing things up? the cars are factory race cars with all of the right ingredients. the only thing they need to compete with & beat a car 35 years newer is a remotely similar power number and updated tire.

Chevrolet used the gear ratios to allow 0-60 without having to shift to 2nd.

What? Maybe with the 2.56 axle but no way with the 3.07s.

None of the C4 vettes will hit 60 mph in first gear, at 4500 rpm with an auto and 2.59 gears you are at 43 mph.

Don't tell me, tell Kevova.

Welcome to the new member !

Yeah, it's not about "torque," it's about power (which damn sure can be directly measured) and traction. The C4 was light with a good-hooking rear suspension and big (for the time) sticky tires, and the automatics generally came with a torque converter that was relatively loose and allowed a good launch. But a 0-60 in the mid 5s isn't all the quick/fast in today's world. The C8 does it in about 2.8s.

This got a bit more attention then I was expecting but my confusion has been resolved still surprised they weighed in at like 3200 pounds!

The C8 does it, exactly… sport mode double click apply brake mash the gas and the car does everything.
The car is really quick and it’s boring, I got tired of mine and sold it. Launch control and an automatic trans 🤢

Yes- what's the point?

I'm not sure how this helps answer the OP's question.

I don’t think he asked what a C8 runs 0-60 either. I was replying to YOU.

He asked why C4s are so quick from 0-60mph. Part of my reply to him is that they aren't especially quick for their weight or power: they run like we would expect a 240hp RWD car weighing 3200lb and with close to 50/50 weight bias and fat/sticky tires would. A quick perusal of Motor Trend's list of 0-60 times will point out that a ton of cars with similar weight/power are similarly quick, including a legion of FWD four-bangers. I should have led with that, but my point with the C8 is that quick cars these days do the deed in half the time. It's irrelevant whether you think they are exciting/interesting or not.

I'd say 3rd, 60 in first gear?

It depends on the year/engine/transmission/axle. I'm sure no 2-valve (L98/LT1/LT4) C4 could run 60mph in first. A 96 LT4 (came with the ZF6 manual trans only and 3.45 axle ratio) was good for 53mph in 1st at its 6400rpm redline. A 93+ LT1 (5500rpm redline) with base 2.59 axle and A4 with 3.06 1st gear could also hit 53mph in 1st gear. I think those were the highest 1st-gear top speeds for any 2-valve C4. The ZR1 with the ZF6 and rear gear but a 7100rpm redline (I think?) gets really, really close: 58.45mph in 1st gear.

All of that's academic, though, because if you really wanted to get the best 0-60 time you wouldn't gear the car this tall at all. You'd probably aim to nearly max out 2nd gear just over 60mph in order to maximize average power over the speed interval.

Which for the record, is pretty damn close to what the 4+3 cars are geared at.

I'm hitting 60 right around 4500 rpm in 2nd when the motor is starting to run out of air.

Technically yeah, you can go a little faster by extending out in to the RPM band, but its really out of air not much above 60.

Oh, that's interesting. I wasn't thinking about the much lower powerband on the TPI cars. So yeah, given the engine's characteristics they are probably geared just about perfectly for 0-60 times.

Good thing you’re here to post what you read about the C8 on motor trend.com Tell us more 😂

They were bad ass for their time, it’s really that simple.

^True.

And in the hands of a GOOD driver, they'll 0-60 faster than the mags have stated. The C4 is a very "driveable" car. Meaning, it's an honest, straight forward driving experience that gives you back exactly what you put into it. So? Well driven, the cars did/do pretty well.

On the flip side...remember when 0-60 times mattered and were a hotly debated/compared thing?? :lol:

Way ahead of the C3 in chassis design and handling. Power? Probably similar at first.

any chance i get to sing the praises of the L98 on the road track, i take.

most guys never take a car to the track (to my surprise!!!!!its a riot!!) but an L98 in the powerband is completely fine on track. Its up to the driver to keep it there specifically on downshifts, learning rev match shifting (i grin every time i nail a rev match downshift that dumps just inside the powerband).

keep it in the powerband right around 3500 and use the 330ftlbs thats there for u. If you have an LT1, you will be doing the exact same thing but the powerband is higher. You as the driver control where you are using your stick.

If you are on a course with a lonng long straight away you will still be fine on a L98 but u will be in a higher gear at the end of it or u will have fallen on your face at 5000rpm. Learn to shift, learn to be quick with your feet.

Think of it like......Tom Cruise in the new TopGun (which is off the charts good)....he was such a good pilot that he knew how to extract the most out of the outdated Jet of his era.

Ofcourse im not saying that an L98 will run with a modern car. But ive personally seen an L98 have far faster lap times than an LS its all about extracting the juice out of the fruit. Technique.

People say L98’s are awesome street cars because you never get out of second gear and barely into 3rd. A street is like a track with no straight aways longer than the stoplight distance. .... just keep the engine in the powerband....and u can go to a decent straight.

Now COTA etc is another thing your L98 will get dusted. Where i live all road course tracks have didly for long straights.

L98 FTW, i love them. They give the next gen of Corvette owners a chance to get in cheap, they are rediculously easy to work on with home depot toolsets. Ive never owned an LT1 or and LT4 but i *really* look fwd to picking one up and learning that platform too. I went straight to LT5 and im in lllooooovvveeee.

And....4+3 rock. So do ZF’s.

:rock: get to the track baby!!!! its an addiction!!

This is the closest to explaining how I understand it. Until you hit straightaways where short-runner engines win on the back-end of the 1/4m, they can hang. In fact, they can win in the 1320 mark. I always thought C4's were in a league of their own (for the day) on auto-x tracks. If they "ruled" on tracks with much longer straight-aways, I'm not aware.

Otherwise, [back then] I gotta think there were plenty of short-runner cars running 300+ HP even if not made in America. Maybe I'm wrong.

OH YEAH....C4's were the first car to hit 1G on the skidpad. They could corner much better than all other cars of their era. And, that's one component of being "fast".

Just my two cents, and it could be wrong, but I do not think power can be measured directly in a physical sense as far as I am aware. Whether we are talking about electrical power dissipated through a resistor, optical power incident upon a photodetector, or mechanical power either translational or rotational, what is actually measured is either an acceleration of a body over time, a force applied for a distance over time, a torque applied for a rotational displacement over time, a photocurrent converted to a power using a calibration factor, or the product of a voltage drop (measured) and a current (measured).
In all these cases power is calculated from the "real" "physical" measured quantities in question.

We've been through this before, yak. Something like "acceleration of a body over time" is literally the direct measurement of power, since power is Work/Time. Inertial dynos directly measure power exactly like this, and they don't need an RPM input to give you accurate power numbers. The do need an RPM input to give you accurate torque numbers, however. Therefore, they are calculating torque using the input values of power and RPM rather than calculating power with inputs of RPM and torque.

I don't really want to hijack this thread any further to go into that.

Measuring the acceleration of an inertial body (roller or translational) over time given a previous measurement of its mass and measurement of the friction losses is a direct measurement of acceleration, not power. Power is then calculated from this direct measurement of acceleration using other directly measured quantities like mass.

Some calculated quantities can be directly measured. I am venturing to say that power is not one of those things. This isn't to say power isn't real. It is a very real physical quantity. Just as far as I am aware there are no direct measurements of it, in the technical physicist sense.

It doesn't have to measure acceleration. It just has to know the change in kinetic energy over the time interval: Power=(K1-K2)/(T1-T2).

I think at this point, it's just a semantic discussion. I maintain that power is directly observable and measurable. For example, if I burn a gallon of gas over an hour of time vs blowing it all up as a vapor in a fraction of a second, the same work was done but the power will be massively different and will feel massively different. But the main thing is that we both understand power to be a "very real physical quantity." Too many people talk about power as some abstract quality that has no real meaning, and follow on to say that an engine's torque output is what matters, and that's just not the case at all.

I think we agree handily!
Power is a critical thing to consider and to "measure".
FWIW in the case of power as calculated from a change in kinetic energy over time, presumably in the case of an inertial dyno, the measured quantity of interest is the angular velocity of the roller.

Wow...I'm almost to my 20th year in this forum. FINALLY someone has figured out the reason TPI's are so fast!

And, here I always thought it came down to the typical argument of HP v TQ!

I agree! The forum FINALLY reveals the truth! "TPIs" are fast b/c they look cool! :lol:

(This thread was actually about C4's)

*sigh* Don't forget, the early L98 C4 was even more impressive when TURNING the steering wheel! For those not aware, back in history, they were banned from the SCCA due to their performance whipping all other cars.

http://showyourcorvette.com/history.php

Thanks for posting that link, Kael. Somehow, the original post -- asking about 0-60 times morphed into what's shown in your link...at least in my mind. That's because talk of TPIs being good cars inevitably results in bashing them because they don't have "horsepower". When someone asks why early TPI C4's were considered "fast", the facts in the SCCA link are what I usually think of. I also think Lingenfelter's Superram played a huge role in early TPI "greatness" -- which is more similar to the "powerband" of an LS intake.

With apologies to Yakmaster, for interuping with my inane scarcasm, the Superram and long-runner intakes are often better for maintaining more power "under the curve" in class events like Auto-x/SCCA. In this forum, mrc24x's racing record is testiment to that. When forum members get to bashing TPIs in favor of the LTx cars, just point them to that SCCA link! If that doesn't work, LSx platform links! LOL All Corvettes are worthy! :thumbs:

Nobody was bashing anything. We were answering the OP's question by pointing out that C4s with stock L98s are exactly as quick as one would predict 0-60mph from their weight, grip, and power.

And your little quotation marks around "horsepower" are exactly what I meant when I replied to yak that too many people believe power is a made-up, abstract concept that doesn't really predict vehicle performance. And that's dead wrong, and he agrees, and he's a physicist. Power is real and, by its very definition, it is predictive of vehicle performance. A torque number is not.

Stock L98 C4s were fast in their day because the competition also didn't have much power. In race trim, they weren't stock and they were making quite a bit more power...as were the competition. In fact, that competition often had it easier because they were turbocharged (e.g. 944T and Lotus Esprit) and could find creative ways to...well...cheat. But the road racing prowess of the C4 had dick all to do with the L98 being a good engine for road racing in stock form: it wasn't. And an LT1/4 would have been worlds better for that.

If you mean the Superram fixed the glaring problem with the L98 by getting rid of the silly long-tube intake, then I agree!

That's simply not true.
Nobody has said otherwise. You're arguing with a straw man.

Quoting from linked story:

"The 1988-1989 Corvette Challenge series came about because, in the Sports Car Club of America's (SCCA) Showroom Stock GT category, Corvette had no challengers. From the fourth generation Corvette's introduction in 1984 through the 1987 season Corvette's combination of superior handling, excellent brakes, sticky Goodyear "Gatorback" VR50 tires and the Small Block V8's power and torque ran away and hid from its Showroom Stock competition."

Stock, not tweaked.

It would be interesting to explore this. The claims made about this topic run the gamut. I've read/heard anything from STOCKITY-STOCK, to 350hp.
Now, here is what this guy knows:
*They didn't race them with cats and I'd bet that they didn't use muff's either. If you watch YT vids of era races, the cars are loud. So... right off we know...that ain't STOCK. They did not drive them out of a show room, and onto the track.
*Conversely, Ain't no stock headed, stock cammed L98 making 350 NET CHP with stock heads/intake/cam. No way, no how, not happening.

MY guess is that they used a blueprinted long block (to me, ""blueprinted" could be interpreted to include head porting and cam timing), open exhaust/no cats, ported stock manifolds, custom tune, and some "Free mods" like a real CAI.

With that in mind, I could buy a claim of ~280 NET CHP....MAYbe a number approaching 300 if head porting happened. But that's pushing it in my mind and a number above that is either boastful fantasy or GROSS CHP.

Documentation showing otherwise, welcome! :yesnod:

Challenge cars had the original engines swapped out for challenge engines during race preparation, the original engines were tagged and "supposed" to be reinstalled at the end of the season.

Uhhh, yeah. Whatever story that is, it's full of shit. They didn't race on stock Gatorbacks in SCCA's Showroom Stock, and they could replace things like the cat-back exhaust, shocks, and brake pads. Hell, we could even replace those things in autocross Stock classes! Besides, this doesn't say anything about how they were/weren't prepped for the Challenge series (which was a whole different thing). I know for a fact that in the Challenge series they used clutch pressure plates with higher clamping pressure and a lightened friction surface...because I had one in my C4. They would have only needed more clamping force if they were making more power than stock, too. My guess is that Tom has it about right.

ETA: It's important to not let this take away from the excellence of the C4 in its day. It did in fact dominate SS while it was still allowed, beating out sports cars from other countries that cost quite a bit more. None of those cars are quick or fast by today's standards, either. In 1990, the SCCA started the Escort World Challenge. The Corvette mostly squared off against the Lotus Esprit Turbo, which inexplicably was suddenly faster on straights despite not being faster in stock form. But when you have a turbo, you can chea...err...optimize things. And the SCCA kept adding ballast to the C4 to give the Lotus a chance. The Corvette still won most of the races. It was just a great road course in every way, and was fast in its day. We should keep in mind that the Ferrari supercar of that time, the Testarossa, still only had 385hp and ran the quarter in 13.5 at 107mph...or about as fast as a new V6 Camaro today.

Quote:
long-runner intakes are often better for maintaining more power "under the curve" in class events like Auto-x/SCCA.
That's simply not true.

Prolly should have said HP limited class events. Back in 2010-2011, I flip-flopped about the use of a hogged out SLP, long-runner intake and an HSR. I sold my HSR to mrc24x who was consistently winning his class in auto-x because the torque (area under the curve) for his TPIS, 350, hot-cammed entry was always faster. He installed the HSR and won a couple of events too. One season later, I bought the HSR back because I thought he wanted to go back to the TPIS intake. If was one reason I ended up STARTING with my modified SLP setup versus starting with the HSR. He was faster until 80mph using the TPIS config. (You know, street car range).

Believe it or not, I still have that HSR 12 years later. Because it was only run in a few events, it still looks close to new.

FWIW, I see multiple websites showing LT1's running 0-60 @ 5.7 seconds....the same as the 1985 TPI (when you "google" it). I also see various other figures including sub 5 sec times with the ZF6 LT1. Probably due to trans gearing. Maybe even diff gearing too? Hell, one website showed a 94 at 5.7 for 0-30, and 13.1 seconds for 0-60 but....wait for it....0-100 at 14 flat. That means the 94 is really, really fast from 60-100mph! You know...less than 1 second! LOL

Still not true. Short-runner intakes like the LT1 make power at higher RPM than the resonantly-choked TPI, but they also have broader and flatter torque curve than the TPI. This is what builds "power under the curve."

"Torque" and "area under the curve" are not the same thing. At all. And if you meant "area of torque under the curve," that's not relevant because torque isn't what determines how fast a car accelerates. Power under the curve is what matter.

Vehicle speed isn't relevant to any of this unless you car is geared so tall that it's in 1st gear considerably past 80mph (which it's not). By the time you have run through the gears once, the car making the most average power (power under the curve) during the run will be ahead if all else is equal. I'd suggest that there were significant flaws in your test, most probably related to tuning and the fact that there were other differences between your cars than just the intakes. The acceleration numbers for an LT1 C4 are better in every speed interval than those for the L98. That's all you need to know. The idea that torque matters more than power at low vehicle speeds is wrong: it's a conflation of some other principles.

The 0-60 times are largely determined by traction and gearing. To accurately compare intakes, you'd need to have two cars with the same kind of transmission and equal gearing.

To me, the point of this thread is: How can a 250hp car be "fast". I don't think you (MM) addressed that. You continue to talk in terms of maximum HP as if you were explaining race theory. Fine. Most members (over the years), could talk about and quantify "power under the curve" and we'd all know that that meant -- and be on the same page. Reading your replies would make it impossible to explain how a 4-cylinder making 250hp probably isn't going to be anywhere near as fast as a TPI making 250hp....especially if the 4-cylinder has to rev 1000rpms higher to get to that power level. I'm not going to belabor the point. You want to derail discussion over semantics.

You say the LT1 accelerates faster at every speed interval than the L98. I disagree. I believe acceleration is fastest when the torque CLIMBS fastest. That's 'what acceration is. It means for that second, microsecond, whatever, it's gaining speed/momentum faster than the second before. Look at the dyno simulation below. One is a TPI-like curve, one is an FFI curve (also a TPI), and the last is an HSR. I used MS Paint to indicate where acceration is fastest. The "upside of the L98 TPI bubble" is also steeper. Yeah, the overall avg HP of an LT1 is better -- assuming you look at the entire useable range (0-redline). In an L98, the redline is lower. Without looking, I'd guess the rpm where it reaches 250hp also occurs at a lower rpm. When you're road-racing or doing auto-x, you might not go all the way through gears. The fact mrx24x was winning in his HP class was torque. You can call it horsepower or power under the curve. When he swapped to an HSR, he had to compete in a class that was 75hp higher....or 100...or something higher. At the end of each gear, sure he was faster running an HSR -- but that doesn't explain the merits of a TPI...or why it "worked" for a street car in it's time.

THE POINT OF THIS THREAD ISN'T TO DISCUSS LT1 VS L98. I THOUGHT IT WAS TO HELP EXPLAIN WHY IT (AS A 250HP CAR) WAS A LOT BETTER THAN MOST (IF NOT ALL) OTHER 250 HP CARS BEFORE IT.

Again...maximum acceleration is indicated by the orange broken line...... And, it doesn't occur with the short-runner intake OR at the highest RPM.
https://cimg1.ibsrv.net/gimg/www.cor...73655d6337.png


Note: if a reader hasn't seen a dyno before, the top 3 lines are measured torque. The bottom 3 lines are calculated HP using torque and RPM. Each one of the HP lines corresponds to one of the Torque lines.

so what does a lt1 a4 2.59 run in the qtr ?

The C4 was absolutely bad ass, 250 horsepower and 340ft lbs of torque was a BIG DEAL. The car was state of the art for its time even the tires were a big deal.We now have idiots writing articles the 1984 Corvette was the worst Corvette ever comparing it to cars that didn’t exist when it was built. Go back and read the press from 1984 about that same car…… IF numbers were all that mattered NOBODY would drive a 1953-1962 and I wouldn’t have sold my C8 and bought another C4 instead.



The roadholding on this new machine is so advanced that we recorded the highest skidpad lateral acceleration—0.90 g—ever observed with a conventional automobile by this staff. That figure practically trivializes the previous high-water marks, in the 0.82-g range, generated by such exotics as the Porsche 928and assorted Ferraris.

Item: It is hands-down the fastest American automobile, capable of 140-mph top speeds, 0-to-60 times under seven seconds, and 15.2-second quarter-mile forays at 90 mph. In fact, these figures qualify the Corvette as one of the half-dozen fastest production automobiles in the entire world!

Then you didn't read my posts here. I absolutely addressed it: an L98 C4 is exactly as fast as one would expect a ~3200lb car with with its weight distribution and drive train layout to be.

Nope. Again, you're either not reading my posts carefully or you're misconstruing them. I have been talking about "average power" and/or "power under the curve" (pretty much synonymous).

Ironically, your own posts show that this is not true at all. Almost nobody seems to understand the concept of power, much less "power under the curve" or "average power" over an interval, and people like you are making this worse! There is a lot of mythology around "torque" and the TPI system wherein many people believe that some horsepower is better or more effective than other horsepower. That's just wrong. The simplest way to put this is: if two cars are otherwise equal (mass, traction, etc.), the car that puts the most average power down over a time or speed interval will accelerate faster. This is by definition of the term "power." Notice there's no mention of torque in there. There's no voodoo. The tractive force that accelerates a vehicle is purely determined by two factors: the vehicle's speed on the road and the power reaching the road. It's just that simple.

It would be impossible to explain that indeed, because it isn't true! A 4-cylinder making an average of 250hp over a time or speed interval would push a car just as fast as the same car with a V8 making the same average power. If you want a real-world example, a 2020 Civic Type R weighs in at over 3100lbs and is rated at 306hp with "only" 295lb/ft of torque. It runs the quarter mile in 13.4 at 108mph, which compares favorably to an LT1 C4 with the same power rating. The C4 may weigh slightly more (stripped-down base models weighed closer to 3200lb than the common 3300lb often stated) but it also has a big advantage in standing-start traction because it's RWD. Again, power is power and the car doesn't care how many cylinders the engine has or what RPM it's turning. It just cares how much power is reaching the ground at any given moment.

This isn't semantics. You're just plain wrong. As I wrote before, power isn't some abstract theory and it sure as hell isn't just semantics. It's a very real unit that predicts how fast an engine can do work.

Yikes! You don't have any idea how any of this works! Not only is this wrong, it might be the wrongest thing I've ever seen posted about power and torque...which is quite a feat! You're just inventing shit at this point. Acceleration is fastest when the most power is put to the ground. Period. I mean...holy shit, Gregg!

The point was to explain why/if the L98 C4 was "quicker" than other cars, not "better." What other 250hp were there at the time? Not many. In 1985, when the L98 came out, the 928S got a bump in power to 288hp. It weighed 3450lb (considerably more than the C4) and still went significantly faster: 14.9 at 102mph. Not much else out there compared to these two cars. The C4 was unquestionably the faster car around a road course or autocross course, for a lot reason not having to do with power/torque. Again, the L98 C4 was exactly as fast as its mass, traction, and power would predict.

Again, no it isn't. You don't know what you're talking about. It's time for you to stop miseducating other people on this and start learning actual physics.


It's relatively slow because it doesn't put down as much average power through the 1/4-mile as an LT1 with steeper gears. I don't know why anyone would really care about this, though: if you care about how fast your C4 is in a straight line, then you don't have one with 2.59 gears!

Quote:

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Originally Posted by JD'S WHITE 93

The C4 was absolutely bad ass, 250 horsepower and 340ft lbs of torque was a BIG DEAL. The car was state of the art for its time even the tires were a big deal. We now have idiots writing articles the 1984 Corvette was the worst Corvette ever comparing it to cars that didn’t exist when it was built.

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All of this is true, and nobody here (including me) has said otherwise. Please try to separate what I've actually written from the things other people have written that have hurt your feelings.

YOU just typed a 400 word response, you’re swearing at Gregg, talking down to other members and now you’re talking about MY feelings being hurt lol 😂

All I wrote to you was not to confuse what other people write outside of this forum with what I've written on it. I'm not talking down to anybody (again, you're misconstruing what I've actually written), just trying to get correct information out there. It's a fact that Gregg doesn't understand this stuff. That's neither an insult nor my fault.

PS - the "400 words" is a result of trying to explain to people how this stuff actually works and how Gregg's ideas about it are incorrect. You most definitely don't have to read them if you find that amount to be excessive!

WRONG! This is where your knowledge needs review.. As a car moves faster and faster, it's putting out more and more power. (Think one gear...say 4th). As you get to the top of the engine's power, the curve flattens. Acceleration slows. It'll be putting out lots and lots of power but losing ability to accelerate faster. Acceleration is not the same as velocity or power.

ACCELERATION (def):
the rate of change of velocity per unit of time

In calculus, accleration is the first derivative of velocity. One tells you how fast an object is traveling, The other tells you how it's speed is changing in that moment in time.

My statement in the prior post is accurate, acceleration is fastest when the slope of it's acceleration is steepest. Don't confuse velocity with acceleration.

Avg power is a different point -- though valid. Avg power can determine velocity at the end of a point in time. Without respect to all other variables, an engine more avg power will be faster, yes. (You have that part right). Up to around 4500-5k rpms, the L98 TPI has more avg power than the LT1. It takes the 4.5k-6k rpm internal for the LT1 to equal and surpass that. So, the amount of average power of an LT1 (which isn't the point of this thread -- but what you want to talk about), is MUCH greater from 4.5k to 6k rpm. At that point, the total avg power shifts in favor of the LT1.

When talking about a 250hp 4 cylinder vs a 250hp V8 Corvette, they will not be equally fast. A V8 that can generate 250hp in 4500 rpms will get to that maximum PEAK hp faster. It can accelerate faster than the 250hp 4 cylinder. THAT is what acceleration is.

It's not b/c of TPI, that's for sure.
The biggest meaningful diff between the 240hp C4 and the last 240hp car that came before it, is TIRES. But any 240 horse, ~3200 lb car will go ~mid to lowish 14's in the mid to upper 90's.....just like a TPI C4.

Continuation of my prior post:
Notice how horsepower keeps rising after torque peak? It's not because the car is accelerating faster. The RATE of acceleration is actually slowing. That's why the horsepower curve FLATTENS as it gets higher and higher. (Eventually, it falls). The amount of power is still increasing beyond peak torque because it is being applied more frequently. (The instances of "BANG" are happening more frequently). The RATE of "BANGS" are happening more often than the "STRENGTH" of the "BANGS". That's power. It's not acceleration.

OK...So put the same tires on a 250hp 4-cyl rice banger and it'll keep up with a C4 TPI. Got it!

Maybe it is putting out more power as it moves faster, maybe it isn't. I don't know why we would think about keeping a car in a single gear: that's never how we actually use a car, especially in a straight-line attempt to accelerate as fast as possible.

Oh, so you actually don't believe that as the moves faster and faster, it necessarily puts out more power (as you stated above)? That's good, because it's not true.

I never said it was the same as those things, obviously. I said acceleration is the result of power applied to a mass. You're the one who confused things when you tried to equate acceleration to the slope of the torque curve, which is some really high-level silliness. To wit:

Quote:

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My statement in the prior post is accurate, acceleration is fastest when the slope of it's acceleration is steepest.

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That's not what you wrote before. You wrote: "I believe acceleration is fastest when the torque CLIMBS fastest. That's 'what acceration[sic] is." Then you proceeded to show us dotted lines on the slopes of both power and torque curves and claim that they represented the point of highest acceleration in the vehicle. That's just wrong. All of it.

Quote:

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Don't confuse velocity with acceleration.

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Why would anybody confuse those things?! I said nothing of the sort. I'm well aware of derivatives and integrations and the difference between acceleration and velocity. The only thing I said regarding velocity is that it's one of the two factors that affects the tractive force that accelerations a wheel-driven vehicle. Power is the other factor.

Quote:

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Avg power can determine velocity at the end of a point in time.

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Yes, and neither acceleration nor power can occur without an interval of time...by definition.

Quote:

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Without respect to all other variables, an engine more avg power will be faster, yes. (You have that part right).

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Good! If you'll just stop there and quit all the nonsense about torque slopes and other goobledeegock, then we can stop.

Quote:

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Up to around 4500-5k rpms, the L98 TPI has more avg power than the LT1. It takes the 4.5k-6k rpm internal for the LT1 to equal and surpass that.

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That's not accurate. We've been over this before. For review, here are GM's own internal documents that Tom400CFI posted in the past:

https://cimg7.ibsrv.net/gimg/www.cor...16fc67db00.jpg


The L98 has more power than the LT1 for about a 1000rpm band around 3000rpm, where it gets a bump from the resonant "supercharging" effect of the long intake runners. Below that the two engines are equal, but that really doesn't matter because we don't see that RPM in an acceleration run anyway. But from 3500rpm onward, the 92 LT1 has more power and that advantage keeps building in big fashion because the L98 peaks at about 4200rpm.

So the power advantage of the LT1 starts at 3500rpm and builds from there. In any kind of acceleration run, you'll never be below 3500rpm anyway. Since the LT1 peaks at 5200rpm on this graph, you'd probably want to shift around 5500rpm. We'd have to look at the gearing, but I bet you'd never get below 4000rpm...which is why the LT1 car walks away from the L98 car.

Quote:

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When talking about a 250hp 4 cylinder vs a 250hp V8 Corvette, they will not be equally fast. A V8 that can generate 250hp in 4500 rpms will get to that maximum PEAK hp faster. It can accelerate faster than the 250hp 4 cylinder. THAT is what acceleration is.

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I wasn't talking about peak power. I said a 4-cylinder engine that puts out the same average power over an interval as a V8 will accelerate the car just as fast if all else is equal. I even gave you a real-world example of a similar-weight 4-cylinder car that has very similar power to an LT1 C4 and is actually even faster! I don't know how you think you can know that the 8-cylinder car will reach it's peak-power RPM faster than the 4-cylinder. That doesn't follow at all.

Wanna bet? You're making the common mistake of assuming the car only has a single-speed transmission. But all modern cars have multi-speed or even continuously variable transmission precisely so they can maximize average power over an interval of acceleration. If you drive a car and shift around the torque peak for a quarter-mile run and then take the same car for another run but shift around the power peak, which run will be faster? The run where you shift around the power peak will be faster because you are maximizing the average power during the run, and power is what determines acceleration.

And BTW, we don't have to guess at this. The C4 gave us the data because although the L98 and Lt1 have the same peak torque, the LT1 has more power and handily out-accelerates the L98 C4.


I don't know what "rice banger" is, but I already showed you an example of a 300hp rice burner that more than keeps up with a 300hp C4.

This is brutal. Greg, you're making stuff up in your head, to support your own bias. :(

1. I thought you were extolling tq?
2. Show us an acceleration metric where the supiriority of the TPI 0-4500 RPM TOWAK, produces faster acceleration? Find a legitimate, apples to apples pair of cars, compare 'em. What is an acceleration metric for 0-4500 RPM? I'd say that's about the 60' mark at the drag track. What do stock TPI 60'? When well driven? About 2.0. What do well driven LT1 cars 60'? ABOUT 2.0. So where's the "more ave power"???
3. No. I mean.....waht are we assuming here? A high revving, small displacement 4cyl? A turbo 4? A 5.7L 4 cylinder? Doesn't matter, really, it depends on gearing, car weight, rotating engine mass..... Optimized for each combo, they'll both get to their power peaks at about the same time.

^This. When going for a basement number, I launch my car at 4000 RPM, slip the clutch and let it hook at the point where the clutch drags the engine down to about 3500 RPM...and I'm off, with a 1.9x 60' time.

1) Not even close.
2) Again, the point where torque climbs fastest IS fastest point of acceleration -- regardless of gear, intake, or whatever.
3) You really think a 250hp 4-banger that needs 5500 rpms to reach that peak will keep up with a 250 V8 that does it by 4500? Interesting. LOL

Both you guys. Since you're set on extolling the LT1 vs answer why a L98 was good for it's day, that's fine. Bye. I think it's ironic you brought Physics into the discussion but don't really know to measure acceleration. You think it's what happens when you push the gas pedal. :D Fine. You'll live great lives with that understanding.

And, yeah, I also understand you're trying to negate any advantage of an L98 by saying "Just rev it above 4k rpms and start from there. Yup...drag racing. Got it. I didn't see ONE SENTENCE explaining why a L98 isn't any faster than any other 250hp car. None.

When people say 250hp car, they mean peak.

But then:
So you really DO think torque - or specifically the rate of change of torque - determines acceleration? So #1 wasn't just close, but dead on. So you don't even know what you're saying! I have to give you credit, though: in the many, many years I've had discussions with different people about power, torque, and vehicle performance, you are the very first ever to say that acceleration is determined by the slope of the torque curve. You are incredibly wrong, but you are creative an unique!

So let me ask you two questions:

1. The definition of power is "The rate at which work gets done," with work being defined for vehicle performance as a movement or acceleration over some distance. So more power is exerted if the distance is longer, the time to complete the work is shorter, or the mass is greater. This is Physics 101, so I'm not creating this out of thin air. Since you say that acceleration is determined by the rate of change of torque (force) rather than power and velocity, are you saying that every physics book in the world has it wrong?
2. William Hay calculated that tractive force (effort) available at the drive wheel's contact patches to accelerate a vehicle is (HP*375)/MPH. All locomotive calculations for performance vs load (especially when having to traverse inclines) are based on this formula. Is this wrong? Is the entire rail industry doing it wrong?

Okay, I already gave you one example that came easily to mind at 300hp. Here's another that's more in the L98 zone: a 2023 VW Golf GTI weights 3154lb and has 241hp with it's four-cylinder engine; and it completes the quarter-mile in 13.6 at 105mph, which is considerably faster than any stock L98 Corvette ever did. Now are you satisfied?

Again, I already answered why the L98 C4 was great in its day and why it is not magically fast but rather is exactly as fast as physics predicts.
Bye, Felicia.
Are you high right now? Really. You honestly think Tom and I don't know how to measure acceleration? It's rate of change of vehicle velocity over some time or distance interval. That's pretty damn simple. And I won't speak for Tom, but if you car doesn't accelerate when you press the accelerator pedal down (assuming it's in gear), then something's wrong with your car. I mean, it's not called the "accelerator" for nothing. This might explain a lot! LOL

Well, then you aren't reading what I'm posting.

See above example of the current VW GTI with 241 peak hp.

Thats their point. Peak HP doesnt actually mean anything in terms of how fast a vehicle is.

If one car makes 250 hp from 4000-5000 rpm and 150 horsepower from 1000-4000, its going to be slower than a vehicle making 250 hp from 2000-5000 rpm. Peak HP is only a generality of how fast a car is going to be, especially when considering wildly different engine designs.

Ugghhhh...That was MY point. ESPECIALLY the first sentence. I said that a few posts ago. and you obviously understand the point. They interpreted by comparison of 250hp engines to mean avg. I meant peak. EVERYONE assumes peak when you reference how much power an engine makes. Unless you specific avg values, of course. THEY are saying any two 250hp engines will be equally fast. That's what I read.

The problem is no one is explaining how a 250 hp TPI wasn't so bad....especially in the late 1980s. Instead I'm pretty sure I was attacked at chastized for suggesting Torque SHOULDN'T BE EXCLUDED from the explanation. It doesn't allow explanation of torque existing at lower rpms translates to lower advertized HP. Differences in torque are how two 250hp PEAK engines can have difference avg HP and different results. Obviously, differences in where the torque occurs makes a difference too.

Too many think Torque is a four-letter word. Let me try.....TORQ! Yup. You're right.
Peace out...
:seeya

Thats because torque isnt a measurement of work. You can get whatever torque number you want with steep enough gearing.

I disagree. Acceleration is the result of a force applied to a mass. F=ma, or in terms of angular quantities T=I*a_{c}
A total change in kinetic energy over a time interval is the result of power applied to a mass over that time interval, which is perhaps what you were trying to articulate, but even that IMO is a sort of butchering of the physics because powers aren't really "applied", at least not in the physics sense as far as I see it. Forces and torques are applied.



The instantaneous value of angular acceleration of a body is most certainly the instantaneous value of of the of the torque curve. Similarly, the instantaneous value of the change in angular acceleration of a body is the instantaneous value of the slope of the torque curve. This is not high-level silliness, it is basic intro mechanics, which I've taught.

This statement I believe to be false. Instantaneous Acceleration can most certainly be considered and measured physically over an infinitesimal time interval, because it is simply proportional to applied force (or torque). Acceleration can occur without an interval or time. Power on the other hand is a calculated (as opposed to directly measured) quantity that requires a non zero time interval over which other physical quantities are measured, and then the values of which are used in a calculation of power.

This is false as stated. It should be restated:
"a 4-cylinder engine that puts out the same average power over an interval as a V8 will on average accelerate the car just as fast if all else is equal."
There is a very high chance that with the V8, there will be sub interval over which the V8 has a greater value of instantaneous acceleration, thanks to its larger values of torque produced.

I disagree with this, and it goes back to our earlier conversation about measured vs calculated quantities. As far as I'm concerned when it comes to causality, determinations of things, and unique solutions to differential equations that specify a particular velocity as a function of time v(t) curve as a solution, power is not what determines changes in acceleration, rather the instantaneous slope of a torque (or force) vs time curve is what determines instantaneous values of change in acceleration. This I believe was greg's "gobbledeegook" point about slopes of torque curves.
I would agree with your statement if you instead had said:
"Calculated average power can be used to calculate average acceleration"

This is not true. The true statement could have been "The car that puts down the most average power over a time interval will have the largest value of average acceleration as calculated over that interval"
The point that I would like to make to you now is that the car that puts down the most average power over time interval might not necessarily be the car that experiences the greatest value of instantaneous acceleration in that interval. That trophy goes to the car with the largest magnitude value in its torque curve, and that is why people like big torque numbers over short RPM ranges. This means a steep torque curve, and larger instantaneous values of acceleration.

I would like to point out here that your language here seems to imply a difference between power and work, and there is no physical difference between those two things.

First I would like to point out that language like "Acceleration is fastest" is really quite poor to use in this sort of technical discussion. Your statement might have been "Acceleration has the greatest instantaneous magnitude when instantaneous power has the greatest magnitude"
But even then, that statement is not necessarily be true. It can be true, but it is not necessarily true. What is necessarily true is "Acceleration has the greatest instantaneous magnitude when instantaneous force/torque is greatest"


First I would like to point out that language like "Acceleration is fastest" and "torque CLIMBS fastest" is really quite poor to use in this sort of technical discussion. Your statement might have been "Acceleration has the greatest instantaneous change to its magnitude when the instantaneous slope of the torque/force curve has its greatest magnitude" and that sort of statement would be entirely and always true, and I think really captures the essence of why people do, should, and ought to care about torque curves.



To sort of bring this all back to reality, I love my L98 car. It wears its "1989C4" vanity plate with pride! Sure I get my doors blasted off on the freeways and interstates by brand new challengers and mustangs, but stoplight to stoplight, onramps, or any other place where the total time interval being considered is rather small, the L98 is able to hang with newer, faster and higher horsepower producing cars thanks to its steep torque curve with large maximum values of torque, which allow the motor (for a given gearing) to propel the car with large instantaneous values in the change in acceleration, as well as large magnitude instantaneous values OF acceleration. Oh did I mention the donuts?

Gregg, I already gave you a comparison on a car with similar mass that was rated at 241hp peak, and its acceleration compares favorably to the L98 C4. What more can you possibly want?! There are almost no production cars with engines so damn peaky that their peak power rating promises more than their average power (under the curve during an acceleration run) delivers. The few that come to mind include a couple Honda VTEC models: the S2000 and the Integra R, and a few shitty turbo cars like the SVO Mustangs that didn't come on boost until about 4000rpm and had such shitty heads that they were all done by 5500rpm. I've ridden a couple motorcycles like that, though, and they sucked. These days there are no cars like that. None.

But you seem to be confusing a low peak power RPM with a broad power band, and that is not always the case. In fact, it's often not the case. The L98 is a good example: it's good power range is basically 3000-45000rpm, and if you end up above or below that you're sucking wind. The SVO is another example. The L98 does not have a broad power band, and its torque curve is much peakier and narrower than the LT1's (look at the factory dyno graphs I included in post #53). The LT1 is far easier to keep near its peak power range, and it will have far more power under the curve and require less rowing of the gears to stay in the fat part of that. The L98 is a relatively peaky engine, but it's peak just happens to be at a very low RPM.

Again, I don't know how many times I have to write this, but I was very clear that the L98 C4 was a great car when it came out. Nobody here has said otherwise. Stop trying to read shit into posts that isn't there and start reading the actual content I posted. This will go a lot better for you if you do that.

Nobody attacked you. We are trying to provide accurate content for everybody's sake. When you're trying to predict acceleration, torque doesn't mean shit. That's as simple as I can make it. The predictive metric is average power applied over the acceleration run. Period. jdjenk just provided the most concise explanation of why this is the case: torque isn't a measurement of work.

Yes, it does. If two engines have the same peak torque but one's is at a lower RPM, then it's making less power and will accelerate the car more slowly. Again, the examples of vehicle comparisons clearly demonstrates this! Why do you keep ignoring it?!
You're just confusing yourself with this. You've been deluded into thinking some power matters more than other power. If you would lose the word "torque" from your vocabulary and just focus on power, you'd be much better off for it.

If you run out of air with the standard TPI, would a SuperRam help the situation? Anybody on this thread tried one?

2. No,
3, LOL, Indeed. Where are the data I asked you for? :bigears: You're the guy who goes to the drag track, and is somehow surprised & mortified that you lost to a same hp 4 banger. But indeed, you lost. Using your argument, a 240 hp Cummins should smoke a TPI, right? B/c, I mean, it "does it by" 2000 RPM. Right? :lol:

Greg, I'll give ya this: You're doing a HELL of a job, rationalizing your own "beliefs". :yesnod: :thumbs:


.

Ah....was THAT what this thread was about!? "Why a L98 was good for it's day".....Hmmmm...nope. That wasn't this thread, that must have been a different thread. I'm pretty sure that this thread was; How were C4's so quick?
Now, I didn't realize that the "TPI"=ALL C4. AFAIK, C4 included L83, L98, LT1, LT4, and LT5. All of which produce about what they should, near the top of their game for their day and none of them have any "magic" in their intakes.

At the other end of the spectrum, why is a 2 liter Honda S2000 so slow with respect to an L98 C4? With similar power (240 hp), 9,000 rpm capability and weight under 2800 lbs. the S2000 looks pretty good on paper.

Broken car, or poor example maybe, but definitely slow in this test: https://www.caranddriver.com/reviews...d-test-review/

I acknowledge that the gearing is not at all optimized for low speed acceleration with the 4.10 ratio. Speed in gear @ 8900 rpm with 832 rev/mile tire: 50 mph 1st gear, 77 mph 2nd gear, 106 mph 3rd gear and 135 mph 4th gear. It really begs for a 5.13 gear to make effective use of all 4 gears (for 1/4 mile and to reach 60 mph at the top of 2nd).

the S2000 was literally one of the two cars I mentioned that may have an especially poor average power through its gear because it's power band is, in fact, quite peaky. However...even as such, it managed a 96mph trap speed which is in the realm of an L98. I'd suggest it's bigger problem was getting an adequate launch with it's peaky powerband and possibly a tall first gear (to make the transmission a close-ratio unit due to the peaky engine), but it seems that once it got rolling a bit it was able to put down some decent average power. Their 0-60 was an abysmal 6.8s, whereas I've seen a lot of those be 1s faster or more. I've seen quarter-mile times for that car closer to 14.0@99, too. Regardless, I never was interested because it is actual work to keep them in their happy place in the power band. No thanks.

Of course F=ma, but we weren't talking about the direct force that accelerates the vehicle but rather what parameter of the engine's output determines the vehicle's acceleration. The direct force (F) that accelerates a car isn't the torque at the crankshaft: it's the tractive force at the driven tires' contact patches, which I've already referred to. That's a linear force, not an angular one. And the only two factors that determine that force, ever, for a wheel-driven vehicle are the vehicle's current road speed (inversely proportional) and the engine's power output at that time (proportional). Ergo, the engine parameter that determines how fast a car accelerates (instantaneously or over some time or distance interval) is the power it puts out (at any given instant or average over the interval, respectively).

Vehicle performance - the topic of this thread - is pretty much always discussed over a time or distance interval. Literally the entire purpose of a car is to move a certain distance, and performance is all about how fast it can do that. Nobody ever talks about instantaneous performance in terms of vehicles. That's just not relevant. The force that's applied to a car to accelerate it (tractive force) is directly proportional to the power the engine is making, not the torque.

No it isn't. It is the instantaneous value of the tractive force curve, but that is a result of the instantaneous power the engine is producing divided by the vehicle's road speed. It is not a product of the engine's torque curve. You are conflating the tractive force and the engine's torque output. They are not at all the same thing.

Gregg was saying that acceleration is directly related to the slope of both the torque and power curves. That's different than the rate of change of acceleration, which is what you're saying. However, again, you're both wrong because you're confusing tractive force with the engine's torque output. They aren't the same thing, and again the tractive force is dependent solely on the engine's power output and the vehicle's road speed. The engine's torque curve has nothing to do with it.

That's fine. Nobody ever discussed vehicle performance in terms of instantaneous acceleration, but this is a more accurate way to state what I was saying.

First of all, if the V8 car has one instant where it's accelerating harder than the 4-cylinder, but they both cross the finish line at the same time, then who cares? They both performed equally well over the interval. Besides, that necessarily also means there was also some time during the interval where the 4-cylinder was accelerating harder than the V8 car. This has to be the case if they both complete the interval exactly the same.

But again, none of that acceleration (instantaneous or average) is determined by the engine's torque output. Regarding engine parameters, acceleration only results from the engine's power output. If you were talking about tractive force instead of crankshaft torque, I'd agree wholeheartedly. But again, tractive effort results from the engine's power output, not its torque. If two cars are otherwise equal and going the same speed, and both are accelerating with an instantaneous 240hp, but one car is making 240hp at 4000rpm with 315lb/ft and the other is making its 240hp at 8000rpm with 157.5lb/ft, they are still both accelerating at the same rate (because the tractive force is the same) even though the first car's engine is making twice the torque of the second car's engine. This is super basic stuff here. As Tom pointed out earlier, if an engine's torque were what determined a car's acceleration, then we'd all be racing Detroit Diesels!

Wrong. Here's the proof:

• A 3000lb car is going 30mph and its engine is making 300lb/ft of torque.
• Ignoring friction and aerodynamic drag, and without knowing RPM or gearing (and thus power), at what rate is it accelerating at that instant?

Or if you want to relate this to the slope of the torque curve:

• A 3000lb car is going 30mph and its engine is gaining 100lb/ft of torque with every 1000rpm increase at this instant.
• Ignoring friction and aerodynamic drag, and without knowing RPM or gearing (and thus power), at what rate is it accelerating at that instant?

The fact is, you can't answer either of those questions because the engine's torque doesn't tell us squat about a car's acceleration. Note that if I substitute power for torque, I can solve the problem without knowing anything about the engine's torque or RPM:

• A 3000lb car is going 30mph and its engine is making 300hp at that instant.
• Ignoring friction and aerodynamic drag, and without knowing torque or gearing, at what rate is it accelerating at that instant?
• The drive tires have 3750lb of tractive force and the car is accelerating at 1.25G or 40.2ft/s^2.

All I need to know is the engine's power output, and it's torque output or curve doesn't matter in the slightest. Knowing the power that reaches the contact patches is both necessary and sufficient to calculate the car's acceleration.

Someone way smarter than me posted these gems awhile back to illustrate both hp and torque vs velocity for a few C4 gear combinations for a specific member's car:

https://www.corvetteforum.com/forums...post1563905394
https://www.corvetteforum.com/forums...post1563916454

Sorry if redundant. The tractive force will directly follow the axle torque (divided by the tire radius) vs velocity, given sufficient vertical tire loading and tire to surface friction. Hope this is clear.

Images from links above:

https://i15.photobucket.com/albums/a...333_vs_373.jpg

https://i15.photobucket.com/albums/a...xle_torque.jpg

https://i15.photobucket.com/albums/a...e_torque-1.jpg

Because racecar (HP*375)/MPH is hard to visualize, but indeed handy.

This is a good and interesting graph that demonstrates concretely how road speed affects the tractive force at the wheels. Also, it shows clearly why torque doesn't directly predict your acceleration: if that were true, then you'd shift to maximize torque under the curve instead of power, and if you look at the graph you'll see how much axle torque (and ergo tractive force) you'd be leaving on the table through a run.

I'll just mention that the two other variables not included here are transmission ratios and (assuming it's an automatic because only four gears) torque converter multiplication at low RPMs. That was obviously outside the scope of the discussion for which these graphs were used, but I'm just noting that there are a lot of variables that affect tractive force.

I agree.
 

I agree with your view. I have one season of OTDs under my belt. So I am experiencing what you are describing. I drive in Michigan at Waterford Hills, Grattan, and once at Gingerman. There were a couple of times at Grattan when I wanted more out of my L98. As in "How did that Carra get down to the end of the straightway so fast." She passed me at the beginning of the straightaway, then instantly was a long way away, as if she had afterburners. lol Where are you driving?

I understand your feedback though I suspect the alternate statement you suggest is too wordy for a general audience. Some of what I said didn't land well either. I shouldn't have entered a discussion like this without better examples and well-worded explanation. I think you can see acceleration means the wrong thing to many people. To you, I tried to send a PM but your mailbox is full.

For newbies, I'll suggest a link to a better comparison to a TPI vs LT1 intake. Actually, the power levels are approximately correct -- definitely closer than the L98 Corvette vs LT1 (with it's higher compression and cylinder head cooling.) When you look at the imbedded dyno comparison, try and imagine the 275hp LT intake lowered to 250hp. THAT'S what you'd might be comparing comparing back in the late 1980's.

Comparing a 250hp L98 to another 1980's non-TPI car might look something like the blue vs orange lines below.
https://cimg9.ibsrv.net/gimg/www.cor...0063c16df7.jpg

Yeah....they orange lines don't cross at 5200 rpms. They aren't real. They are just proposed lines for the purpose of demonstration.

Gregg, I don't know what you're trying to say with all this graphed stuff with imaginary lines on it. You still don't get it: the acceleration of a car is not linked directly to the engine's torque output or the slope of the torque curve, but rather to the car's tractive force at the contact patches. Tractive force is the force that accelerates the car, and it is directly determined by the power reaching the wheels and inversely by the car's speed. Period.

:flaghalfmast:

That’s for this thread, the OP has 4 posts total
and has left this thread 🧵

IDK why. Was it the fantasy world of DATSUN's or the fantasy world of TPI TORK monstah's?


For a meaningful demonstration, the data needs to be something that could actually happen in real life. Fantasy data helps nobody.

I'm down to learn a thing:
In any given gear, I blieve max acceleration will be the point where the engine is at max tq. NOT where the tq curve slope is steepest, but where it is totally flat; at it's PEAK. The engine is creating the most possible rotational force that it can make....transmitted through the gear ratio, through the diff to the tires it will create the highest tractive force (in that gear).

In this scenario, the acceleration is greatest at 3200 RPM (TPI) or 4000 RPM (LT1) in a given gear....however, the power reaching the wheels would be highest at about 4000 RPM (TPI) or 5100 RPM (LT!). Thus my confusion.
Now if we had a CVT....

This is true, 100%. But...

A CVT is the perfect example to think about this. If you have a CVT and it's set to hold the engine at maximum power during WOT, it will accelerate faster than if the CVT were set to hold the engine at max torque instead. That is, the tractive force would be greatest at any particular speed with the engine held at peak power instead of peak torque. Why? torque multiplication through the transmission? For the L98 in the factory graph, the peak power comes at 25% higher RPM than the peak torque, but the torque at 4000rpm hasn't fallen by 25% yet. So at the peak power RPM, there is more force at the driveshaft/wheels, even though the engine's torque output is lower at that RPM. If you never shift, you won't experience this as such: just know that the greater power output is being "soaked up" by the great road speed: remember that tractive force is Power/RoadSpeed, and again, the road speed at peak power RPM vs peak torque RPM has increased more than the torque has decreased.

In the world of conventional transmissions with discrete gear ratios, you'd see this manifest as shifting to maximize "power under the curve" vs "torque under the curve." If you shift just after torque peak at, say, 30mph, then you will have reduced the engine's leverage over the wheels. Whereas if you shift just after the power peak, you keep the engine's greater leverage (numerically higher total ratio) over the tires beyond 30mph. For the L98, you'd still be in the lower gear up to 37.5mph, which is 25% faster, and yet the engine's torque output hasn't fallen by 25% yet. Ergo, the tractive force is higher and you accelerate harder at 37mph than if you'd shifter earlier.

Copy. Those two lines were the crux of what I wasn't wrapping my brain around. Using percentages to show the speed vs. tq helped to visualize it more easily, too. :thumbs:

The CVT is an easy way to visualize "perfect world" for sure. We "clutch" snowmobiles to run WOT a little above their peak hp rated RPM....and not their peak tq RPM for the reasons that you stated.

I was trying to figure out a way to write that so that it made some kind of sense. Glad it worked! I have to remember for the next time I get into this discussion with someone (and there will surely be a next time).

Now, just to add one more layer to the understanding and kind of bring it full-circle: when you start talking about staying in the lower gear for longer, and how that means less torque but more multiplication leverage to get more force at the wheels, you may also realize that you're also talking about more engine RPMs. Ergo, when you talking about gearing and torque you are really using more/different verbiage to refer to power (because torque*RPM=power=MPH*TractiveForce). And it starts to sink in how the metric of power wraps all this complicated interaction between torque and gearing and MPH into one neat number that fully describes the rate at which the engine can accelerate the vehicle (and/or what top speed it can drive it to).

Industrial, ship, and aviation specs always talk about power exclusively because that's what determines the rate at which an engine can do work. They never squawk about torque unless they need to know how to spec a drivetrain to withstand the motor's force. If you want to know how fast a pump can move a fluid, you need to know the motor's power, not its torque.

This is quite the thread. To answer the OP……..The stock L98’s and LT1’s were quick in the day but those days are over. The amount of time spent on this topic is mind boggling.

Go take a C6 or a C7 out for a spin…….Take care!