Dyno Numbers

[nikitopo]

Going to a 4.1 final drive ratio was a marketing decision, but I suppose the complete 4.3 rear diff should be swappable

[ZDan]

Originally Posted by nikitopo

Lol. Peak power is just a single POINT in the power curve. It doesn't work like this in reality for 1/4-mile trap speed.

It pretty much does work, quite well. Not perfect but a good first approximation.

It might be a very rough estimation of what you 'll get, but nothing else. What it really matters is the power you have in the complete rev range and this is also dependent to torque.

Of course power is a function of torque, but again, power is *more information*. If you known engine torque and vehicle weight, you know nothing, you can't say what acceleration performance will be. If you know *power*, you have a pretty decent idea what 1/4-mile trap speed will be. And for *sure* you have a very good idea how two similar cars with similar overall engine output characteristics compare.

Don't you like the word torque I said? Just change the word with power under the COMPLETE power curve.

Torque is torque, and power is power. Torque is static moment = force*distance, but power is the *rate* of doing work. Torque by itself can't tell you about acceleration potential, but power can. Torque is NOT "power under the COMPLETE curve". If you have either curve, over the rpm range, you have the other. But if you *only* know peak power (and vehicle + driver weight), again you still have a good approximation of trap speed. And if you *only* know peak torque, you have no idea.

[nikitopo]

Nit picking topics. Noone said about peak torque. Would you have the same 1/4-mile trap speed with a turbo car having same peak power? Can you have a simple formula to fit all the cases? Answer is NO, because with turbo you can have a much more flatter torque curve. Same about NA engines since each one has a different torque curve. We are not in the 80's or 90's where a simple formula usage might be okayish. We can have nowadays detail simulations with pretty much most of the parameters that count. But anyways, it is pretty funny going always to the very basic discussions.

[Dzmitry]

Originally Posted by nikitopo

Nit picking topics. Noone said about peak torque. Would you have the same 1/4-mile trap speed with a turbo car having same peak power? Can you have a simple formula to fit all the cases? Answer is NO, because with turbo you can have a much more flatter torque curve. Same about NA engines since each one has a different torque curve. We are not in the 80's or 90's where a simple formula usage might be okayish. We can have nowadays detail simulations with pretty much most of the parameters that count. But anyways, it is pretty funny going always to the very basic discussions.

Well technically your torque curve in a turbo engine would likely not be flat at all! But in any case, power is still the defining factor. The reason a 1/4 trap time is likely faster in a turbo car of about the same weight compared to an NA car is because it has more POWER through most of the rev range. But, if you were to actually take 2 very close examples (very similar weight cars with very similar peak power, same drivetrain, same tires, one turbo, one NA), I would guarantee you the 1/4 trap will actually be quite close. That's because once an NA car gets going, it spends most of its time at the peak of its power band, where it will match the turbo car acceleration.

[nikitopo]

Pfff. Zdan has an ACE350 header and not an ACE150 or 250, because it gives the best results under curve/ all over. It is not just about what peak power you make. So too much talking for nothing. Do you want to feel that new car is 210whp or 220whp or whatever? You are free to believe it. I am sure that something special is hiding inside this new engine

[Frost]

Originally Posted by nikitopo

Pfff. Zdan has an ACE350 header and not an ACE150 or 250, because it gives the best results under curve/ all over. It is not just about what peak power you make. So too much talking for nothing. Do you want to feel that new car is 210whp or 220whp or whatever? You are free to believe it. I am sure that something special is hiding inside this new engine

I think you're missing the point of all of this techno-babble.

Power is important but that doesn't mean torque isn't. They are two sides of the same coin.

[Dzmitry]

Originally Posted by nikitopo

Pfff. Zdan has an ACE350 header and not an ACE150 or 250, because it gives the best results under curve/ all over. It is not just about what peak power you make. So too much talking for nothing. Do you want to feel that new car is 210whp or 220whp or whatever? You are free to believe it. I am sure that something special is hiding inside this new engine

Of course. No one is saying more torque doesn't help down low. It is certainly very nice to have that power curve start rising quickly at low revs. ZDan was just making the general notion that you can certainly relate the cars peak power, weight, and drivetrain to quarter mile runs and trap times.

I actually dug up a quick example for fun. There's obviously other factors such as tires and all, but this is still a pretty decent comparison.

2008 BMW E92 M3
RWD
HP: 414
TQ: 295
Weight: 3650
1/4 mile: 12.7s @ 113mph

2019 BMW M2 Comp
RWD
HP: 405
TQ: 406
Weight: 3560
1/4 mile: 12.4s @ 114mph

You can see how closely related these come out to be, despite the M2 having a whopping 111 more lb-ft of torque, a slight weight advantage, and likely slightly better tires.

[Frost]

Originally Posted by Dzmitry

Of course. No one is saying more torque doesn't help down low. It is certainly very nice to have that power curve start rising quickly at low revs. ZDan was just making the general notion that you can certainly relate the cars peak power, weight, and drivetrain to quarter mile runs and trap times.

I actually dug up a quick example for fun. There's obviously other factors such as tires and all, but this is still a pretty decent comparison.

2008 BMW E92 M3
RWD
HP: 414
TQ: 295
Weight: 3650
1/4 mile: 12.7s @ 113mph

2019 BMW M2 Comp
RWD
HP: 405
TQ: 406
Weight: 3560
1/4 mile: 12.4s @ 114mph

You can see how closely related these come out to be, despite the M2 having a whopping 111 more lb-ft of torque, a slight weight advantage, and likely slightly better tires.

SIDE NOTE: I'm also struggling in classing the newer modern turbos compared to turbos pre 2010 in OTA. These new cars make gobs of torque for longer too.

[ZDan]

Originally Posted by nikitopo

Nit picking topics. Noone said about peak torque.

Here's what you originally said that I take issue with:

Originally Posted by nikitopo

Not sure why you mix and match 1/4 mile times with peak power numbers. In such timings it is torque that matters the most and not peak power.

Well, no, it isn't. Power is what is important. I would totally agree that the shape of the power curve *is* important, but even if you only have a peak number you have a decent guess at 1/4-mile trap speed. Particularly for an NA car. And for sure it's a very good basis for comparing the claimed hp for the new car vs. the old one as their power curves are fairly similar. The new car does have a more "filled-in" power curve so if anything scaling by cube of 1/4-mile trap speed should give a slightly higher estimated peak hp relative to the previous generation.

Would you have the same 1/4-mile trap speed with a turbo car having same peak power? Can you have a simple formula to fit all the cases? Answer is NO, because with turbo you can have a much more flatter torque curve.

Akshually... What most modern turbo cars have is a much flatter POWER curve, not torque curve. High-strung NA engines typically will have a flatter *torque* curve which gives a PEAKY power curve that rises somewhat linearly up to a rounded point before falling off.

Simple formula is a rule of thumb that correlates quite well for NA cars in particular. Modern turbo cars that make very near peak power over a very broad rpm range, a modified formula would work better. But hp = (trap speed/234)^3 * weight is pretty damn good for our NA cars.

Gen 1: hp = (95mph/234)^3 * (2800 + 165) = 198hp
Gen 2: hp = (101mph/234)^3 * (2840 + 165) = 241hp
+22%! Not bad...

For grins, and to demonstrate that it's not "torque that matters", let's rewind to a couple of early 90s Corvettes (L98 and LT1) that gave close to the gen1 and gen2 1/4-mile trap speeds, with roughly TWICE the torque:

1991 Corvette L98 rated at 250hp, 350 lb-ft, 3380 lb. curb weight, 96mph in the 1/4:
(96mph/234)^3 * (3380 + 165) = 245hp (98% of 250hp rating)
https://www.caranddriver.com/reviews...mparison-test/

1992 Corvette LT1 rated at 300hp, 330 lb-ft, 3330 curb/3480 test weight, 102mph in the 1/4:
(102mph/234)^3 * (3480) = 288hp (96% of rated)
https://www.roadandtrack.com/new-car...-corvette-lt1/

There is no such simple quick/dirty approximation using TORQUE, because it is not engine torque that matters, it is POWER.

Power/weight (within reason) pretty well determines performance. YES, power curve MATTERS! But "torque/weight" is meaningless and tells you nothing, whereas power/weight does. The formula myself and many others use works quite well for NA, and it wouldn't be hard to develop one for turbo cars with a much flatter power curve. Formula I'm using will tend to overestimate "peak" power for such cars.

Same about NA engines since each one has a different torque curve. We are not in the 80's or 90's where a simple formula usage might be okayish. We can have nowadays detail simulations with pretty much most of the parameters that count.

It was easy enough to model vehicle performance in the 80s/90s as well! No different today. The "simple formula" is just as good a quick/dirty approximation today as it was then.

But anyways, it is pretty funny going always to the very basic discussions.

Fun for me

Originally Posted by nikitopo

Pfff. Zdan has an ACE350 header and not an ACE150 or 250, because it gives the best results under curve/ all over.

I got the ACE350 because it was available used for semi-reasonable $$$$ vs. new price, and my friend and competitor in time trials had gotten a Tomei EL for his '17 86. So I figured if he zigs, I zag, and it worked out great FWIW I wouldn't have pushed the button on the header if I hadn't had a couple/few high-gravity double-IPAs...

It is not just about what peak power you make. So too much talking for nothing. Do you want to feel that new car is 210whp or 220whp or whatever? You are free to believe it. I am sure that something special is hiding inside this new engine

There's nothing magical in there. +20% more displacement = +20% more torque, and same peak power rpm suggests +20% power as well. And lo and behold it looks like that's about what we get. With another maybe +2% "magic". Kick-ASS!

[timurrrr]

Originally Posted by nikitopo

What it really matters is the power you have in the complete rev range [...] power under the COMPLETE power curve.

If we're talking about 0-something acceleration (whether time or speed), the bottom half of the rev range doesn't matter at all.
As long as you have a good launch and don't bog down the engine, the revs will never be in the bottom half when you're power limited (as opposed to traction limited).

[nikitopo]

Originally Posted by timurrrr

If we're talking about 0-something acceleration (whether time or speed), the bottom half of the rev range doesn't matter at all.
As long as you have a good launch and don't bog down the engine, the revs will never be in the bottom half when you're power limited (as opposed to traction limited).

Not really. Shifting @7300 1st to 2nd drops you @4400 rpm. So, you are in the middle rev range where 1st gen had a bigger torque dip. No wonders why the 0-60 mph time drops from 7.0 to 6.0 seconds with the manual. People saying that it has a 20% increase in peak power (meaning 205hp*1.2 = 246hp catalog power and not 228hp) simply don't see that torque starts to fall @6500 rpm. Check the Delicious Tuning torque curve (not numbers just the curve). If engine could hold torque till 7000 rpm, then yes it would have this peak power number but it doesn't. It is what it is with the new engine. It has much better launch times, but power levels start falling after 6500 rpm.

[Varelco]

OK I think this thread has been sufficiently derailed enough. Feel free to carry on through PMs. The rest of us want to see and talk dyno numbers.

[soilent]

Originally Posted by Varelco

OK I think this thread has been sufficiently derailed enough. Feel free to carry on through PMs. The rest of us want to see and talk dyno numbers.

Completely agreed. I don't want to see anymore posts unless it's dyno graphs and discussion thereof.

[s30series]

Originally Posted by soilent

Completely agreed. I don't want to see anymore posts unless it's dyno graphs and discussion thereof.

Completely agree.