Originally Posted by joe731

OK,

I've done a little research and believe that since HP is a function of Torque and RPMs (i.e., HP = Torque * RPMs/5252), the goal is to keep the car in the max HP range as much as possible.

That said, for my car, and most 996TTs the peak HP comes between 5,000 and 5,500 RPMs (562 at the wheels). This was true before my turbo upgrade/tune and after as well, though it is worth noting that after the tune the peak HP curve is flatter (longer) at the top, which is a good thing. After 5,500 RPMs my peak HP starts to tail off as Torque fades reducing to 530 by 6,000 RPMs and it holds pretty steady from there to redline. Conveniently as you will see in a moment, my HP is 530 at 4,500 RPMs.

So, with that background, ideally I want to manage my shifts so that my upshift does not take my next gear RPMs minimize the HP drop above 6,000(530hp). Since HP at 4,500 is conveniently 530, I want to shift when the upshift will result in next gear RPMs above 4,500.

My transmission gear ratios now come into play to determine what the RPM drop will be for each upshift. My X50 tranny is stock, so from the owners manual I get:

1st = 3.82
2nd = 2.05 (53.7% of first)
3rd = 1.41 (68.8% of 2nd)
4th = 1.12 (79.4% of 3rd)
5th = 0.82 (73.2% of 4th)
6th = 0.75 (91.5% of 5th)

Playing this out for shifts between 5,500 and 7,000 for each gear, I get the following useful information:

Shift 1st to 2nd at 7,000 and end up at ~3,757 RPMs, lower than you want, but at redline

Shift from 2nd to 3rd at 7,000 and end up at ~4,815 RPMs

Short shift from 3rd to 4th at ~ 5,700 RPMs (peaked at 530 HP) and end up at ~ 4,525 RPMs just above 530HP

Short shift from 4th to 5th at 5,500 RPMS (peaked at 530 HP) and end up at 4,510 RPMS just above 530hp

Short shift from 5th to 6th at 6,000 RPMs (peaked at 530 HP) and end up at 4,500 RPMs at 530 HP

All of this assumes want to continue to accelerate for at least a few more seconds, i.e., ignores the lost acceloration of the shift time.

I am a bit surprised by the short shifts to 4th, 5th and 6th, but that's what my math says. Does anyone see flaws in this math? It seems to be a product of flat peak HP between 5,000-5,500 with drops on both sides of that range.

I am happy to be told this is wrong if you have math or other facts that make the case.

Thanks all