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Rob 930 Rob 930 is offline
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Join Date: Dec 2002
Location: Seattle
Posts: 660

I had a 915 gearbox in my car for awhile. In contrast to others' advice, I'd suggest it would be fine to give it a try -- especially since you already have one. I loved the gearing; in my opinion it was much better than stock 930 gearing -- which, for my purposes, was worthless. The 915 first is pretty short, but if you consider it a gear just to get started with, second through fifth are great. The problem with the 930 is that the spacing between the gears is too wide. This is solved with the 915. On the track (which is my interest), even the 930 first is too short to be useful. Then there's a huge, lag-inducing gap between first and second. To cap it off, the 930 fourth was too tall to be useful to me under any circumstances. On the 915, first might still be too short for any significant driving, but the other four gears will be perfect, unless you want to go faster than about 160. Yes, it's a little buzzier at highway speeds (because you lose the super overdrive of the 930 fourth gear), but for most fun excursions, I think it's very nicely geared. After all -- it's just the same as a 911.

Yes, the 915 may not be as strong as a 930 box, but even for track use, if you put it together right and treat it with respect, it should last you a while. If you mod the engine to a significant degree, you might want to be careful, though. If you're interested in drag racing starts, or anything that shocks the drivetrain excessively, then forget about the 915. But if you're one who will apply the power smoothly, it should be fine. I know a local road racer who used one with his 500 hp EFI engine very successfully for several seasons. Once he upped it to about 550 hp, he started to break 3rd gear and went to a G-50. If you're going to install a 915, I'd consider at least putting a temp gauge on it (you can do this easily by modifying the reverse light switch to become a temp sender location). That way you can monitor the temps and decide if you need extra cooling. For street use with a few blasts on boost, you'll probably be fine. On the track, you may need more cooling.

To install a G-50 is so expensive that it can't really be considered an alternative to the 915. Unless you want to spend $10-12K to convert, I'd consider the 915 to be a viable option if you want five gears. It sounds like you have an aluminum 915, probably with the 8:31 R&P, which is the best 915 to use.

As far as installing it, it should go in without too much trouble You need a 915 shifter, which just bolts in. I think the shift rod that goes through the tunnel from the shifter to the transmission is identical, but you might want to verify that. The halfshafts just bolt on, as I recall; I think the flanges and bolt patterns are identical. The trick is to get the transmission mounted fore-and-aft in the right location. Neither the 930 nor the 915 stock front mount will work without modification. I can't describe the best way to make this happen; you just need to get some help from a fabricator (if you're not one yourself). My front mount was based on a 915 mount, but it had to be moved about 3/4 of an inch either forward or backward, as I recall. I may have flipped it 180 degrees to help make it reach. In so doing, it interfered with my rear sway bar, which was a small problem. What's important is to locate the transmission so the halfshafts and shift linkage are in the correct locations. That means the engine will be in a different location -- and will be farther forward by about 3/4 of an inch, I think. To accommodate this, I had to make a spacer for the rear engine mount, and use longer bolts, so that the crossbar mount stood rearward from the engine by that amount. The clutch cable worked fine, as did the throttle linkage. All the oil lines, fuel lines and wiring reached just fine. I think the rear engine cavity seal barely touched the rear tin, though. For a clutch, try Kennedy Engineered Products, in California. They make a clutch for the 225 mm 911 flyweel that worked just fine.

Good luck.


Last edited by Rob 930; 06-28-2007 at 03:45 PM..
Old 06-27-2007, 04:51 PM
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