915 Transaxle and Torque

This came up in the supercharging discussion, but I think it merits its own topic. In upgrading engines (via supercharging, turbocharging or swaps), does there come a point where you stand the risk of ruining the 915?

I have read that the 915 was designed for a maximum of 300 Nm of torque. I know that the engine I just mated to my transaxle puts out more than that. Are there any horror stories out there of stripped trannies? Did different versions of the 915 have different limitations?

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Jack Olsen
1973 911 T sunroof coupe

the magnesium case was used from 72-77 and the case can break or the main shaft.

In 77-78 the input shaft size was increased and the case material was changed to alum. in order to hold up to the new 3.0 engine.

At that point (78- ) your weak links became the clutch holding power and relativly short gear ratios for higher HP engines.

hope it helps,

s


[This message has been edited by H20911 (edited 10-15-2000).]

Jack,

Bruce Anderson's 'Handbook' shows several 915 gearboxes modified with an electric pump to filter the gear oil and squirt oil on the ring & pinion, and gear clusters ... in application with Turbo engines.

It might also be time to consider SWEPCO 210 gear oil with extra moly ... intended for overloaded gearbox applications.

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Warren Hall
1973 911S Targa

Swepco 210 it is, then, at least as a first step. Any idea on sources? I don't see the heavier duty stuff on the Zims site.

Actually, having done a quick search, I also see Swepco 212, which is listed as having added Molybdenum Disulfide. Is this the one I should put in there?

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Jack Olsen
1973 911 T sunroof coupe

[This message has been edited by JackOlsen (edited 10-15-2000).]

Jack:

With my 2.7L race motor (approx 250hp) I had the 915/12 (7:31) tranny rebuilt with a kevlar clutch disk and a taller 5th gear. Oh yeah - I needed a new case as well! Old case was fracked. Flywheel was fine but I'll probably wish I had coughed up the extra $s for an aluminum one.

I am told that this 915 tranny should be more than capable of handling the power.

This 911 will primarily be a "sleeper T" street car - and I have been told that a tranny cooler was not needed.

Best to you,

Kurt
http://www.911restorations.com

Kurt

Did you put the 2.7 engine in the 72 T on your webpage? That is a beautiful car -- I think I first saw it when you had it listed on eBay a while back. Really great photography of it, as well.

What difference does the 5th gear make? What's the rpms, for example, at 70 on it? And have you tested for a top speed? That's the only area where I'll miss the taller ring and pinion, although I don't know where I'd ever test it out. My insurance is bad enough as it is.

I have a 1978 930 which has had a 1986 915 transmission since 1993 with no problems. There is a shop here in California that does these conversions regularly without problems. I have been told not to stand on first gear ..... which I have not, and there have been no problems. The transmission is a little noiser than the 930 box, but 5 speed is much more driveable than 4.

[This message has been edited by garrickl (edited 10-16-2000).]

Jack:

Thanks for your kind words. I must say I spent a good hour admiring your car at your website and enjoyed the information you provided.

I hope to have answers for you before Christmas regarding my 911.

The mods are currently being performed.

Motormeister is doing the work - and yes I have read every thread in here about these folks!

So far, my experience with Roy has been great and I will keep you apprised of the project. Because this is a high $ project, I have been told that Lee is building this engine himself.

The proof will be in the pudding, so to speak.

Best Regards,

Kurt
http://www.911restorations.com http://www.starnes.com

The longevity of the 915 in high performance applications depends directly on how it is used (or abused) by the driver. I have a buddy who modified and dragraced his SC. 191HP to the rear wheels on 245 wide tires with a posi resulted in 2 scattered 915 trannies. If you put out more than 200 ft/lb of torque AND plan to drive it hard expect problems. On the other hand, a turbo is easier on the tranny than a supercharger. SOOOOO - if you have a supercharged SC and you want to get all you can out of it you may want to consider a 930 tranny.