915 tranny Options

[john914somers]

So I'm starting to change my 3.2/901 914 race car into a 3.6/915 and I am wondering if an older magnesium case 915 with a 7/31 ring and pinion will hold up? Any opinions are greatly appreciated! Thanks a ton!!!

[Jeff Hail]

A late aluminum case 915 should be fine for a 914. Flipping the ring gear is a simple procedure and normally just requires relieving the case for the bolt heads. I have seen a few 915s that didn't require any shaving. I do recommend the steel bearing retainer and its a fairly inexpensive upgrade but well worth it for longevity. When you flip the ring.. gear walk or thrust is now going the opposite direction so replacing the side cover with a stronger type is not necessary. The standard taper bearing on the cover side will be fine with the ring flipped. For a 911 I do recommend the stronger side covers along with the 930 taper bearing modification as history dictates many failures from thrust. The case wall is plenty strong for mid engine application.

Inverting the 915 upside down (not flipping the ring) will require work and change the height of the drivetrain. Additional lubrication modifications are recommended for longevity since the main shaft and stack are now sitting differently in the oil bath. The 915 was not designed from the start to be run upside down. When set up properly they work well but expect to pay for mods.

For a street car you would need to add a Hall sensor to the trans to run the speedo correctly. Its really easy to add this. Would need to pick up a 911 speedo and change out your old mechanical 914 meter.

There is a lot of gear options for the late 915 that are very suitable for a 914 with the engine you are planning. In fact a long first and second gear can be a lot of fun with that motor.

The 930 option is a different animal. It was designed for torque from birth. Parts and mods are significantly higher but the payoff is strength. You do not see many 930 failures like its smaller cousins in light weight cars. The 930 is close in weight to the 915.

901, 915, 930 are all good units. Just depends on what you want out of them and what engine is in front of it. When torque levels go up service life goes down. Shifting has always been the number one issue on all of these. A properly assembled box will shift fine. These boxes are showing age and they will operate based on the technology at the time they were designed.

Like anything if you maintain it it will last. If you race it expect to spend some duckets to keep it fit.

Last you will need to figure out your shifting solution and axle adaptation. Lot of options out there.