Improving Performance With Shorter Tranny Gears?
 

Ok the stock 5-Speed in my 1969 912 is in need of a rebuild. I know a lot of folks in the 911 world have their transmission rebuilt with shorter gear ratios by places like Powerhaus.

What I am wondering is when I have my transmission rebuilt could I have shorter gears put in for better acceleration? I mean I would never go over 90 MPH in the car anyways so why not make it hit it redline in 5th at about 90-95mph?

Would I need to have all the gears replaced with shorter gears or just a few of them or what would be the optimum setup?

I know I had a stock 91 Mustang GT Automatic with 2.73 gears I replaced them with some 4.10s and it was a huge increase! Can I get that percentage of a gain on the 912 or am I just wishful thinking?

The stock ratios in the 912 box are pretty short as it is, with a stock 5th gear you should be hitting 4k rpm at 70 mph. If the car will be exclusively tracked or autocrossed, I would suggest putting a shorter fourth and fifth gear. I believe the stock 3,4, and 5th ratios are M, S, and X. If the car will be street driven, I would say to reuse the stock ratios.

Efrain
68 912 Coupe

I would keep the stock gears. The engines last a lot longer at lower rpms, and on a stock engine you won't get much of a performance gain with lower gears.

I know it's tempting, but I'd stay stock - I think the 5sp with the 4cyl. is about as good a combination as you can get for all around useable performance. As an alternative for autocrossing, etc., you could grab a set of used 14" wheels with 50 profile tires & effectively get a shorter ratio setup. The 911 (especially the later ones) have enough torque and a broad power range to take advantage of variations, but, aside from specialized racing ratios, those don't always improve on the factory's stock ratios.
Just my 2-bits.