915 race transmission mods?

[petevb]

I’ve got the transmission out of my early 911 because I managed to frag the Quaife differential. While it is out I’d like to upgrade. I’ve already got a wevo shifter, 7:31 ring and pinion, and I’m planning on a PSJ or other coupler. The car makes about 255 hp out of a 3.2, and splits its time 50:50 between the street and track.

I’d like people’s experience: what makes a noticeable difference, and what order should I do the modifications in? I’ve heard about the Wevo shift gate and turbo synchros. On the other hand I’ve also heard that I should just put it back together stock but “well adjusted”. I’m mostly interested in helping shift speed and feel- I’m used to 951 and other newer gearboxes. My budget is not unlimited, so I’d like to get opinions on what mods give the best bang for the buck. I posted this on Rennlist as well, but it seems quite...

Thanks for the help.

Pete

[Jack Olsen]

Well, there are a lot of ways to spend money on a 915. If lap times are a big priority, then shorter, close-ratio gearsets will feel like an extra 30 horsepower. If transaxle life is important, then a cooler is vital for extended track use, and a spraybar is a good bonus. The Wevo internal gateshift will make your shift selector feel more precise, but it is on the pricey side. And if you're more into tracking than autocrossing, then the ZF differential is considered the smarter choice, since it helps you under braking as well as accelerating. Replacing the side plate with a later model aluminum one (or billet aftermarket piece) will also help.

Then again, if you're going to spend money on a 915, you might want to buy an 8:31 box, and put in shorter (and closer) gear sets. My 8:31 has a lower max speed than my 7:31 did, but it's much more robust transaxle overall.

[moazam]

Originally posted by petevb
The car makes about 255 hp out of a 3.2,.....

Not to get you off topic, but how did you get 255hp out of your 3.2? Chip+Exhaust+NoCat+?

[petevb]

Thanks Jack,

The box was an ’84, and the PO swapped the 8:31 out (which I still have). You are saying that at my power level I should be worried about blowing the 7:31 up, and should consider putting the 8:31 back in and doing a whole new gearset…(?) What should I expect this to cost on top of a rebuild, which I’m doing anyway? Would you do the 8:31 and gearset first, or the wevo shift gate?
Already doing the ZF and cooler.

Anything in different synchros or something (I noticed you did turbos on your car)? I can’t help feeling like it’s all going to go back together and it will still be a slow box…

BTW, if anything my problem now is that I need a taller box- I can top it out (rev limiter, never mind redline) on the longer straights).

Thanks again…

Moazam- I wish I could tell you exactly what it’s got for engine mods, but I bought it this way. The PPO did at least headers, sport exhaust and a chip (unknown type) to a very late (’89 engine code) US 3.2L. The car put down 224 at the wheels on a dyno that has seen a bunch of similar carreras. None made close to that power (it dynoed similarly to chip and exhaust C2s), so the mechanic thought was that something else (cams?) may have been done to the motor as well.

[surflvr911sc]

Tyson installed a one piece bearing retainer in my aluminum transmission, in prep for a 3.6.

[Speedy1]

If the 915 tranny is rebuilt with HD parts " that is generic for I'm installing a 3.6L motor so beef it up, and used on the street only. Will it survive every day commute of 10 miles a day for many years to come?

[Randy Webb]

moazam -- it's not hard to get 250 hp from a 3.2 -- mine has mild street cams and dynos at 250 with ruler flat torque -- carbs, 10.2:1 twin plugged and a few other mods.

[moazam]

Originally posted by Randy Webb
moazam -- it's not hard to get 250 hp from a 3.2 -- mine has mild street cams and dynos at 250 with ruler flat torque -- carbs, 10.2:1 twin plugged and a few other mods.

Nice...I have the SteveW chip on order so that should give a small kick.

Actually, I'm not even that high on getting more HP out of my 3.2. I figure after my transmission is shifting properly, I'll be able to shift right and the car will pull harder faster.

Anyways, back on the topic...is there a FAQ or doc that explains all these 915 transmission modifications (gear ratios, etc.) and what they're about?