R&P question

[Bob Harriman]

Which is better? Is there a downside with the 6:29 compared to the 7:31. I have a 901/13 which is a 911 trans in my 912 but have the opportunity to purchase a 902/06 with a 6:29 R&P. I'd like to do a rebuild myself to learn hands on and then I won't have to remove mine from the car but if the 902 with the 6:29 is less desirable, well, forget it. The 902/06 is a late 69 912 which is what my car is. The 902/16 looks to be identical R&P and gearing. Both 69 912.

I know it's a 912 question on the 911 forum but I get more info on here. Sorry ESR's.

Thanks, Bob

[edmayo]

The 6/29 was a hill climb ratio, not meant for longetivity. The small pinion has a higher wear rate. Probably okay for an occasional use car like yours. To do the proper set-up does require some special tools.

[Bob Harriman]

The seller of the one I'm considering says syncros were rebuilt 10K ago but sings noisily at 55/65 MPH.This site has all the hillclimbs as 901 with 7:31 R&P.

http://www.blueskymotorsports.com/in...id=17&Itemid=6

[edmayo]

Yes, hill climb gearing was also done with the 7/31. Its ratio was 4.42 to 1, the 6/29 is 4.83. Much lower geared. Ask Gordon Ledbetter, he is an expert on these.

[Bob Harriman]

It is actually a 902/05 with an X 5th gear and a 7:31 R&P. I'm going to pass though. I run 55 series tires so the X is too low for the hwy. My Z is 76 mph at 4K rpm as it is. Any lower won't work for me. The bluesky website doesn't even list a 902/05.

[911pcars]

Bob,
FWIW, early on, I unknowingly upgraded from a 4 to 5-speed gearbox which turned out to be a factory 6:29 with the commensurate hill climb ratios. In 5th, engine was spinning at 4,000 at 60 mph - a little much for flat land cruising with 110 hp. Later on, I "downgraded" to a more mundane 915.

Sherwood

[gled49]

San Francisco dealers sometimes installed the lower R&P in 912's so they would go up the hills. Very fragile pinion gear, so small. Gordon