Shifting RPM Dilemma
 

First off I'm talking about a stock RX-8's engine w the horsepower peak at 8500rpm, and peak torque at 5500rpm.

I noticed that by shifting up, the rpm drops by 2000. If I would change my driving style to shift at about 7500rpm instead of going to redline, wouldn't I be going faster by being in the peak torque range longer? (I'm assuming I don't want care too much about the peak horsepower range, because hp is just a derivative of torque and therefore not as important to acceleration as torque.)

Can somebody give me some input on this?

proper shifting is individual to each car and is a skill that is learned by practice.
If you're trying to eek out every last bit of power then maybe a track guy can come in here and give you some stock numbers to go by, but your car is still going to be different.
Here's a good post from Eric Meyer: https://www.rx8club.com/showpost.php...2&postcount=14

If you're looking for smooth shifting and a smoother acceleration curve, just keep practicing.

you need to know more than just peak numbers, the Renesis torque curve is rather flat

http://www.datsuns.com/Tech/whentoshift.htm

Rear wheel torque = engine torque X gear ratio

Engine RPM = speed * gear ratio * a constant

HP = torque * RPM * a (different) constant

so a little math says that maximum acceleration (RW torque) in a given gear will occur at the torque peak, and maximum acceleration at a given speed will occur in whatever gear gets you nearest the HP peak.

In the RX8, this basically all amounts to shift at redline.

guys i was kinda looking for more of a direct answer.

laythor - you seem to misunderstand my question. I know proper shifting technique, I'm asking about the engine.

TeamRX8 - the article pretty much supports my hypothesis, i just didn't take gearing into consideration. i'm just taking a 2k RPM drop after shifting as a constant for all gears. from what i have seen, the assumption isn't too far off, and i have noticed the power begins to taper off after 8000rpm anyway, so i think in general i have the right idea.

the goal I've always heard from the fast people (and fast car builders) is to shift into the same horsepower level you shifted out of in the gear before - the idea is to maximize the amount of the power peak you use (ie maximize area under the power curve used)

I saw a pretty good article on that. I had posted it in the RX-8 general sub-forum. Basically, for optimal acceleration, you want to shift when the wheel torque (or hp, it doesn't matter which you use) in the current gear is equal to the wheel torque of the next gear. This takes into effect gearing as well. That way you are putting the most amount of power through gearing down to the wheels as you can.

From what I saw, going to about 9,500 in first is optimal. Will I be doing that much? Nope. I'm going to stick to 8k or so, just to save engine life. On the track though, I might. Still, all the serious people on here that know rotaries say that 9k is too high, so I'm going to try and take that to heart.

100% not true. power is what matters. power is indeed derived from a torque measurement, but as Team hinted, torque can be manipulated through gearing. power cannot. a 200hp, 100ft-lbs engine can make any amount of torque you want at the wheels (i.e., where it matters), but will always make only 200hp.

in layman's terms, ask yourself why a diesel VW, weighing ~3000lbs and making ~140hp/240ft-lbs is not faster than, say, a Civic Si, weighing ~3000lbs and making 197/139. if torque was all that mattered, the VW, with its ~100ft-lb advantage, should be loads faster.

this article lays it out very well:

http://www.vettenet.org/torquehp.html

anyway, you want to shift at or around the car's power peak (basically, redline in an RX-8). try it both ways and see which is faster.

i believe the rev change from gear-to-gear is a percentage, not a constant number; i.e., shifting from 2nd to 3rd at 8000rpm will drop the revs more than shifting from 2nd to 3rd at 3000rpm. think about why that drop can't be a constant number.

It is a percentage. It's the difference between the gear you are in, and the gear you are going to. So if 1st was 3:1, and 2nd was 2:1, it would be a 66% difference. Shifting at 9k in first would bring you down to 6k in second.