I was flipping through some old posts on clutches (pending my clutch job on the Callaway 944) and I ran across Chris White stating that the early 931 trans were desired for their 911 G15 gearing interchageability and due to their strength. Hence this perked my ears up. The Callaway is an original 83' 944 but now has a 951 longblock but still retains the original IHI turbo, etc and uses a 951 intercooler. From Callaway the engines put out 285hp and I anticipate I have a bit more due to the MAP sensor, better intercooler, and freer flowing exhaust. Anyhow, with my clutch job starting up I was interested in knowing if it would be worthwhile to swap out my standard early 944 trans with the 80' 931 style? As of know the current trans is holding up fine, but the stock NA clutch would slip under 3rd-4th gear pulls even at 0.5BAR. Would this be a direct swap?? IIRC the gears now lie ahead of the axle much like the 908/03's hence the snailshell design. And IIRC isn't this a "dogleg" first setup? A good firend of mine has two 931's and one snailshell trans sitting in his garage currently.
Thanks for the help!!

 

the early 931 tranny has 915 guts....strong yes, but the synchos and shifting leave MUCH to be desired. remember that it isn't the hp that kills a tranny, it is the torque. the calloways always used stock tranny's in all their conversions...they lasted well with it. I have had a few calloway turbos of various types...944 and vw and they never had any issue with trannys. i suspect that it was because of the inherant lag they had in those days in the turbos. I think you will be opening a very unneeded can of worms with wanting to use that unit...besides, what torque tube are you gonna use? if you clutch slips , it isn't up to snuff. they used a high pressure modified pressure plate and a grippier sport style disc on the calloways as i recall (at least stage 2 vw's did)

 

Thanks for the post Nick, as I got to reading more about the 80' 931 tranny over on the 924.org site I was convinced that this was more work for little benefit. I was always kind of confused why when the 2nd owner on my car put the 951 block+head in they never upgraded the clutch to the larger 240mm 951 clutch. The first year I owned it the clutch never slipped but as I started dialing it in (it was a mess tuning wise when I got it) the NA clucth started to give up and it still specs out new for wear. Car has 32k miles and engine has about 3k miles. I am planning on going with a setup from Markus Blazak up in Ontario who provides a 30% increase clamp force pressure plate and his stage III Kevlar disc that will together hold ~425hp. I bet the turbocharged VW's are a blast to drive! Do you have any pics of your Callaway cars?

 

G31 trans is actually the strongest one in the whole 924/44/68 line-up, but as stated already, it has weak 2nd gear syncros. Get the syncros new (if totally worn, probably the "dogteeth" need to be replaced too) the shifting is ok even on redline and without using clutch (I've done it).
It's much lighter too than Audi-based gearboxes, weighn app. 2/3 of the Audi-type gearboxes.
About 915 parts interchangeability. 3rd, 4th and 5th gear are the same design, 1st and 2nd are NOT, so are syncros, they are different.
Syncros of 4th and 5th are interchangeable between themselves and are the same as 915 gearbox.

It holds up fine until 450-500hp but an oil cooler should be used.
When converting to G31, you'll need a torsion bar carrier of an 924/931 that uses G31, becuse it has special mounts for it. G31 trans is much shorter: ends with differential (the gearbos is ahead of rear axle contrary to regular Audi-style boxes).

EDIT: G31 has special torque tube, so it must be changed too. Clutch is 225mm like 944 one.

 

What's the difference? Pics?

 

Difference is in mounting to the gearbox, as the G31 doesn't have that huge bellhousing that is rudimentary feature of all Audi-type boxes.