911 SC 915 short ratio diff options ?

[stv951]

Hello all,

I am considering installing a short ratio crown wheel and pinion. My target is in increase the mid range torque characteristics on a 911 SC with a 3,2 engine.
We are not interested in top speed, but this is not a race car, so something in between would be nice. The car is driven alot on narrow hillclimbs


What options do we have for the 915 gearbox ?
7.31 ?
8.31 ?
8.35 ?

Any ideas ?

Thanx

[Bill Verburg]

Originally Posted by stv951

Hello all,

I am considering installing a short ratio crown wheel and pinion. My target is in increase the mid range torque characteristics on a 911 SC with a 3,2 engine.
We are not interested in top speed, but this is not a race car, so something in between would be nice. The car is driven alot on narrow hillclimbs


What options do we have for the 915 gearbox ?
7.31 ?
8.31 ?
8.35 ?

Any ideas ?

Thanx

W/o more info it's hard to say,
tire sizes
year of the transmission
rev limit
is cruising rpm an issue

in general 7:31 w/ a stock SC is going to be very short and 8:35 will be intermediate between stock and 7:31 but closer to the 7:31. The drops of course are unaffected by cwp or tire changes

for an 80-83 RoW w/ 245/45 x16 tires top speed stock
7:31 ~139
8:35 ~141
8:31 ~159

[gumba]

A bunch of years ago we had our '84 trans w/8:31 converted to a 7:31 with the addition of a early 5th gear (not sure what year). This coupled to a 3.2 w/Steve Wong chip, SSI's and sport muffler. Swapping out the r&p made a huge difference at the bottom end, and up through the mid range. A great improvement coming out of slow corners at the track. The early 5th gear keeps the motor in the 3200 rpm range at 75-80 mph, using 245/45/16's on the rear. This set up is now in my VW bus and works great for the street.

[Trackrash]

Read here for more than you wanted to know.
Has anyone used the 8/35 ring and pinion?
short gearing

[Matt Monson]

Thanks for bringing my attention to that 8:35 thread. Mbe posted some inaccurate infirmation I had not previously seen.