[RickB]

There are two new magazines at the newstand, with Cooper S tests. One of them (Motor Trend, I think) has a sidebar about the different approaches taken by manufacturers to get 100hp per liter. They plotted the power curves, and made comments about the power delivery. The Cooper S and Beetle 1.8T had virtually identical acceleration figures, even though the power delivery couldn't be more different.
The Cooper S builds toward 4000rpm, then is very flat from there to 6000. The Beetle builds similarly early on, then drops off, then spikes at high rpm.
My question: Since the rate of acceleration of the Cooper S is highest just above 4000rpm, and actually is declining from there to redline (based on the graph), is there any reason to rev the engine higher than whatever engine speed would correspond to 4000rpm in the NEXT gear? That is, the car accelerates as fast or faster from 4000 to 5000 as from 5000 to 6000, so why bother winding it, if you can keep the engine in a 1000rpm window?

[jlm]

the torque vs rpm curve flattens out (constant torque) from around 3500, but the power vs rpm keeps on increasing at the same upward slope until it hits the rev limit. the 1000 rpm window is a good target, but what seems to get the most power is to redline it in each gear before shifting.

[RickB]

Max power is at 6000, so you are not getting an increase in power by winding it higher than that. It seems to me, that the reason for winding most engines past their power peak, is to keep the engine from dropping out of the power band after the shift - the car is still accelerating faster in whatever gear you're in, than it would after a shift. With a 6-speed tranny and a very flat power curve, I don't know if that's the case. Why shift at 6750rpm, dropping the rpm to, say 5750 in the next gear, if the car accelerates faster in the 4050-5050 range?

[jlm]

the power curves i have seen show power increasing until the redline/rev-limiter cuts it off steeply. the torque is flat until red-line as well. the implication is that the power would continue to climb if not shut down by the rev limiter, although one would assume that the flat torque curve would start to fall off anyway as the breathing/engine efficiency starts to degrade.

if your engine can last spinning at 7500 (and the rev limiter allows it), you will have considerably more power than at 6000. even though the torque may be falling off.

i did a search on "horsepower vs torque" and found a curve or two from mini madness in the evotech chip upgrade post.

[DaveNagy]

Quote:

Why shift at 6750rpm, dropping the rpm to, say 5750 in the next gear, if the car accelerates faster in the 4050-5050 range?

I believe gearing trumps all other factors. You pretty much want to stay in the lowest gear you can, for as long as possible, even if this takes you "away from" the peak power band in both the current (low) gear, and in the new, higher, gear. The important thing is that you are making the most of that lower gear. (Ideally, you'd never get out of first gear. Alas, we don't live in an ideal world)

-Dave

[PigLick]

Quote:

Originally posted by DaveNagy

(Ideally, you'd never get out of first gear. Alas, we don't live in an ideal world)

-Dave

That's what CVTs are for

NOTE: Just a little fun, I know very little about this subject and don't mean to start an off-topic debate in this thread, its interesting reading.

PigLick

[minimini36]

For the MCS the fastest acceleration occurs if the engine is taken to the redline in each gear. I did an analysis using the torque and horsepower curves that appeared in the Technical Article about the MCS drivetrain. There is a link here on Mini2.com to this excellent article. The peak horsepower occurs at 6000 rpms and does not continue to increase past this point. Some of the dyno runs show that it continues to increase past this point and I believe this is a result of how most chassis dynos measure horsepower. I then used the gear ratios in each gear to determine the acceleration in each gear at various engine speeds. It was always better to stay in the lower gear because shifting to the next higher reduced the torque to the wheels and dropped too far down the power curve. Remember shifting to a higher gear may get you to the peak torque of the engine but the transmission will be multiplying it by a lower number. The lower the gear in the transmission the more it multiplies the torque. I believe I posted the tables from the Excel spreadsheet over on roadfly.com. If I can find them there or on my home computer I will repost them here.

[Andy@Ross-Tech.com]

I measured and plotted the acceleration for my GTI 1.8T:



Somewhat non-intutive shiftpoints of 6500,6700,6200.

I'll do the same for my Mini Cooper S.