951, 968 transmission swap

drfatz · 10-01-2004, 09:13 PM

I recently purchased a 1985 1/2 944 NA. I have done all the engine upgrades possible without changing the crank and keeping it NA. I am looking to auto-X the car, but would like a little more acceleration. I am planning on gutting the car and putting in some fiber glass and new suspension/brakes are on the way. I have done some homework, but am unable to find the gear ratios for the 968 6 speed transmission, does anyone know them? Also will this give my car the much needed acceleration in 1st and 2nd gear? I don't really care about top speed or street use, this is a purpose built car. Finally how hard is the swap to do, and is this what I should be doing seeing as it also has a LSD? I have read that either the tach or spedo sending units are different and may need to be changed. Any help would be very much appreciated.
Cheers,
Graham

carsontc · 05:46 PM

you'll find the specs here:

http://www.porsche968uk.co.uk/Porsche_968_Technical.htm

speedometer on the 968 is driven by the right front wheel ABS 'hall' sender

you'll probably need an aftermarket electronic speedo set up which involves attaching magnets to the axle shaft, adding the sender and calibration. must be someone who has done this somewhere...dunno

(btw...the 944 transaxle sends 4 pulses per revolution of the hall transmitter to the dashboard)

also the axle shafts are different lengths (left v right)

might be other considerations...I seem to remember someone talking about needing to modify something else.

drfatz · 10-02-2004, 08:47 AM

Thanks for the link. So here is my next question....if you have 5-6 gears and then a final ratio...how does that work. Say you are in first gear with a 3.600:1 ratio and your final drive is 3.889:1 .....what is the engine rpm vs axle rpm (the only thing that really matters)? Is it just 7.489:1?
-Graham

drfatz · 10-02-2004, 09:30 AM

One other question, what about swaping out the 951 transmission for a 931 5-speed? Are the 931 transmissions any good? I know that they were developed by Porsche rather then VW and they have a lower 1st and 2nd gear :-)
-Graham

carsontc · 10:49 AM

see:

http://www.924.org

and for transaxle ratios see tech section:

http://www.924.org/techsection/7transaxle.htm

(assume you have MS Excel)

tifosiman · tifosiman's Garage

Quote:

Originally posted by drfatz
One other question, what about swaping out the 951 transmission for a 931 5-speed? Are the 931 transmissions any good? I know that they were developed by Porsche rather then VW and they have a lower 1st and 2nd gear :-)
-Graham

You have an 85.5, right? The 931 trans won't bolt up (easily) and won't have the odo drive. The 951 trans will have too high of a final drive ratioin in the R&P gears.

If you are autocrossing an N/A, the best gear ratio will be found in an N/A trans. Unfortunately, the weakest R&P is also found in the N/A trans pre-1988. You should plan on seeking out a 1988 or 1989 N/A transmission (they have stronger R&P gears and less reported failures, Porsche changed the spec to ROW transmissions for 88 and 89). Or, consider upgrading your current trans to a hardened R&P from Powerhaus II.

PM me if you have any questions. I seem to have become the unfortunate expert at destroying N/A transmissions in a car that is autocrossed frequently............