How to build a Ultimate 915 trans for a 3.2 using 912E/915 cases + oem oil cooler

[Blackbyrd]

I'm curious

I've been reading as many post as I can on 915 transmissions

but really see the same stuff written or just little snippets here and there


I have a 915/68
1st gear: 3.18 (11/35)
2nd gear: 1.83 (18/33)
3rd gear: 1.26 (23/29)
4th gear: 1.00 (26/26)
5th gear: 0.79 (38/30)


Ring and pinion: 3.88 (8:31

I also have a factory 915 Oil cooler (not mounted)


I plan to use this to help cool the transmission so I have to keep the aluminum center section.







Currently driving the 915/68 with my 3.2 engine and 17in wheels, My first gear is a little hard to get into when rolling all other gears are great but still notchy. so Im planning to take it apart.

I'm looking to improve my 915

I have a small collection of 915 transmissions available but need some help to maybe make an awesome combo

I have:



915/70 (same gearing so I'm going to skip this one)
and a 923 912E as well as a unknown early mag transmission not pictured

(all numbers are grounded off the early trans so I can't tell)

A 915/63 is in the photo but was sold.

So my goal here is to

Save weight
gain a little more torque
as well as all around improvement


I use the car mostly for Street driving
The car is practically my daily driver so I have to keep that in mind.



My question are

Would it be a good idea to switch any of the aluminum pieces from the

915/68 to Magnesium ?
Nose cone ? Bell housing ?


Would it be smart to use smaller gears ?
Should I switch over to a 7:31 ring and pinion over the 8:31?

I don't plan to buy an expensive billet side plate

or aftermarket gears, just normal items to refresh the transmission.

No plans of an LSD yet (unless someone has one here)




Any help would be appreciated

[will hung]

The shorter final drive will increase the torque available to your rear wheels but at the cost of ultimate strength.

The 912e gearbox is cool in that it's the only magnesium 915 case that has the casting piece for an electronic speedo.

I'm currently getting the 915 rebuilt for my SC. I've kicked around the idea of sourcing a 912e gearbox for it's 7:31 R&P and mag case. My car is mostly used for street driving, and the combination of a 7:31 R&P with the SC's gearing would make 5th a usable gear. Additionally, the tracks near me wouldn't allow you to fully use 5th the way it's set up now, so shortening everything is beneficial to me. May hurt the gas mileage on road trips though. I keep deciding against it for a combination of added cost and the fact that the mag case saves only like 12 pounds.