Gargamel

We're talking about straight line here. What's going to result in getting from point a: to point b: the quickest? Do we shift at peak torque or do we shift at peak horsepower?

rynberg

That should be pretty easy for you to figure out. Do you think a stock car would be faster shifting at 5k rpm or 6.5k rpm?

Depending on your gearing, you usually want to shift PAST the power peak, in order to hit the power area for the next gear. Look at a few recent threads with posts by JimLab, he's made graphs showing this.

Gargamel

This graph, I've seen. I've gotten both answers so this is why I ask. You're saying shift during peak power but right before power starts to drop, correct?

KevinK2

In most cases, the FD should be shifted at redline. I made an excel ss to plot rwtq vs speed for all gears, and it's clear redline is best for engines with flat hp curves at high rpms. An old V8 with peak hp at 60% redline would likely have gear specific shift points.

Gargamel

I'm needing answers for a modified FD, large frame turbo and basically stock ports.

KevinK2

answer should be same, hp curve would be like your stock FD curve with less power at low end where it doesn't matter. got a dyno run?

jimlab

You don't shift at peak torque or at peak horsepower. You shift at the point at which torque at the axles (flywheel torque x transmission ratio x differential ratio x 0.85) in the current gear falls below what torque in the next higher gear would be. The result is something that looks like this.



If the torque curve for the current gear crosses the line for the next higher gear you shift at that point (the last two data points are 7,500 and 8,000 rpm in this chart). If they don't cross (1st and 2nd gear, for example), you hold the gear to redline (8,000 rpm in this case). It's that simple.

The funniest part is that you posted today in a thread where this was explained.

https://www.rx7club.com/showthread.p...71#post3550071

1QWIK7

iTrader: (33)

i agree with the above

unless you are faster than an automatic shifter, shifting a little past peak will be more better.. that way, you fall in the powerband in the next gear..i would also check the powerband of the car as well as gearing as said above..

Gargamel

Only thing I got out of all this is basically shift around 7,800-8,000 instead of 8,600 like I've been doing.