Yargk

Yup

GTgears

Someone PM'd me that I had a technical oops on this post. The 2.7 runs a 1.46 3rd, not a 1.48, though that doesn't change the math I actually ran since I had the actual toothcount input into my gearchart. I use a 7400 rpm shiftpoint because these are street cars and track toys and in my experience most owners don't rev to the rev limiter in that application. Given those parameters, the upshift to 3rd is at 5250, which is the basis for my "barely" 5000rpm...

It's better than stock, but still far from optimized.

jmartpr

I really like the idea of using a 2.7 transmission....you would still upgrade 3-5/6 and LSD. In case you have a failure you have your OEM GT4 transmission stock which still has warranty.

Bill Verburg

Here's what is and what could be, stock GT4 vs GT4 w/ PDKS
These graphs take into account the stock GT4 torque curve, wt and aero

GTgears

Been hoping Bill would come along.

BillC3

Very interesting that 2nd gear in the manual GT4 is about equal to 3rd in PDKS.

Manifold

Similarly, 3rd in the manual isn't far off 4th in the PDK-S. Beyond that, acceleration is less in absolute terms, so it matters less.

This all fits the subjective perception many of us have that 2nd and 3rd are too long (arguably, 1st also).

cmosman

Bill, Great chart. I had seen one of these (yours?) on a different board. It would really be helpful to the discussion if you could play back the difference between GT4 stock and GT4 with 2.7 transmission. The ratios are in post #123, left column.
Also, I assume the sheet plots v(t) as well. That would be interesting, too!

Thanks so much!

Yargk

Hi Bill, been reading your posts on Pelican for probably 15 years. What would be nice is another chart that shows the difference vs. speed and third chart showing the integral of that difference chart vs. speed.

Mech33

Cool! Acceleration vs speed is enlightening but I think power vs speed is easier to see the overlap differences. The intersections of the acceleration vs speed and power vs speed curves are of course the same (if you take into account aero power consumption).

Mech33

Maybe % difference vs speed to make it easier to interpret?

Yargk

Yeah, that'll work

Warwick Morris

Looking at the excellent graph, I would have thought a lower final drive would be a good move for the GT4. It's a lot simpler to replace the crown and pinion than strip down a gearbox and should be a lot cheaper in labour though obviously the gears will be expensive. Hopefully someone will make some parts in the next year or two.
My 996.1 GT3 (never sold in the US) has a cup car FD in it and it's a rocket ship and you have a good time changing gears a bit. It's like adding 30-40 BHP. BTW that car also runs an aluminium flywheel and small diameter twin plate race clutch which enables the engine to accelerate RPM quicker.....and I raised the rev limiter to 8500 (which is just an on/off software switch 7800/8500 on that model).

GTgears

It's a transaxle. It comes all the way apart for a final drive replacement. About twice the labor of gears.

stout

Hello all,

Matt was kind enough to send this my way for review, and it is great info. I wonder if the max rpm should not be lifted to 7800 rpm (I know they're street cars, but I do extend to redline from time to time, and it is instructive to see the true max speed in gears).

But, herewith for further discussion: