d230

Can anyone reccomend a gearset for my 915 tranny? It has the 7.31 r/p, but is otherwise stock.

I would like to have gearing where if I shift at 5,000-5,500 RPM, the engine will not drop below 4,000-4,000 RPM.

TIA

Cupcar

If you can get your hands on a copy of the the book Up- Fixin der Porsche Volume VIII available from PCA website, here: <a href="http://www.pca.org" target="_blank">PCA Website</a>. There is a nice article in it: "The Designer Gearbox", by Russ Dickerson, on page 62 that addresses exactly this question.

Dave Banazek

That's a pretty closely spaced gear box. The spacing is more in line with a motor that revs to 8,000 rpms and has a 2000 rpm power band. Most of the stock engines have a much wider usable power band. The other questions you first need to answer are what top speed do you need? Do you need a first gear for around town? Are you willing to spend $1200 to get a first gear that is really only good once you get rolling? What size tires do you have? I have a gearbox that tightly spaced. You would burn up a lot of clutches on the street and top speed with an 8000 rpm redline is about 140mph.

If you want to figure out your own setup I have a spreadsheet to do it. Email me.

d230

Thank you, Dave. Currently, I use 60-series tires, but will go down to either 55 or 50-series this summer.

The top speed I'm after is about 130 to 140. But I'm not as much interested in top speed as in off-the-line and mid-range speed. 120-125 would be my minimum.

Currently I have a stock SC motor (except pre '75 exhaust) mated to the 915.

I'll email you. Any help would be greatly appreciated.

Thanks in advance.

JackOlsen

You should put your car on a dyno and verify where it's making maximum torque, and start making your gear decisions from there.

C Streit

Not sure why you'd want to shift at 5k-5.5k RPM though, can you explain?