OK, well I have worked out a place that supplies low compression 3.0L 16v pistons, so my next question is about the transaxle.

I figure I'll be shooting for 330 - 350 HP at the crank, so should I use an S2 tranny or swap in a 951 tranny? I assume the 951 tranny would have better gear ratios for a turboed motor, but which one can take more power? Which one will be reliable with that much HP, and an upgraded clutch?

 

The transaxles are the same as far as strength. Gear ratios are a little taller on the 951 trans and they also have a trans cooler. The S2 trans would be fine for a turbo car.

Where did you find the pistons and how much were they?

 

Apparently Heritage Motorcar sells "968 16v turbo pistons 104.5mm" made my Mahle, so I'm assuming those would work for an S2 as well. If not Mahle, JE, and Weisco all take custom orders, so either way, its doable.

Theoretically, what is the top speed determined by the gear ratios in both the S2 and 951 tranny?

How high does the speedo measure in the S2 - in other words, is there room for growth on the top end? Of course, top speed is not my goal here, I'm just curious....

 

I believe that LSD is going to be a bigger benefit than higher gear ratios. Once you add power you will want to be able to apply it to the road instead of spining the wheels. So if you have a choice of transaxles I say go with the one with LSD or the one with the highest percentage LSD.

 

Bruce, I had not thought of this, although it makes perfect sense. However, as long as you're spinning the wheels, you aren't snapping your drive axles....

Was the LSD a fairly common option on the 951s or S2s? I know its quite rare to find one in the n/a ones.

 

I believe it was an expensive option. But if you are going to build a turbo then you might as well spend the time to find a tranny with LSD. The standard 968 LSD was a 40% lockup, the 968 Turbo S had a 70% lockup.

There are new third party LSD units available but they cost a few thousand so a used tranny may be the cheapest route to get one.

I am sure Raj can give you some pointers. He has a 968 Turbo S transaxle in his car!

There were two options in the 968 transaxle, a Porsche manufactured clutch type LSD in the earlier cars and a Torsen LSD in the later cars. I understand that the clutch type is better for track (high speed) and the Torsen is better for AutoX but have no data to support that. I have a 40% Torsen in my 968 Cab and love it. I can floor it in a straight line without having to worry about wheel spin, although the tires can be chirped going into second and third. Never tried to chirp them in fourth. In the corners I can use the right foot to provide oversteer but it is very controlled.

 

Sounds good; however I don't think I'll be attempting to fit a 968 tranny into a 944 S2. I suppose I'll just look for a 951 or S2 tranny with an LSD and pay whatever needs to be paid to get it.

Pete, forgot to mention that it does not list the price of the pistons on the site, and I still haven't found anyone who has an idea on how much a set of custom pistons would cost. I suppose I'll call around and let yall know when I find out.

 

LSD was a LOT more common on 951s than it was on S2s. Either tranny can handle the power you're looking for. You might want a stronger clutch to go with it though.