slate blue

Carl,

Is there a compromise made regarding exhaust clearance behind the transaxle? It seems that the Corvette diff housing is much longer than the Porsche's.

FLYVMO

Very nice Carl!

Looks like a quality piece! Keep up the good work.

Cheers!
Carl

Carl Fausett

Slate Blue - Good eye!

In post 171 I displayed a picture that shows how much room remains between the end of the diff and the fuel tank. It isn't that bad. We emphasized getting the transaxle as far forward as we could. Moving the weight that is behind the rear axle to in front of the rear axle lessens the moment of polar inertia when cornering, and the angle that the CV joints have to make up so we also lower torque lost through them. Also - as you observed - we need to clear the transverse pipe on a dual exhaust that runs from the RS to the LS.

That picture will help you to see how far forward we were able to position it. The limit is where the CV Joints hit the cross-member - that's where we have to stop.

This car has the Motorsports SS dual exhaust on it, and we intend for it to go back up. That's why you see we have located our transaxle mounts in and up out-of-the-way; to make room for the dual exhaust and also to keep the polyurethane mounts away from the heat of the pipes.

We would like this kit to be compatible with all our other kits, and that includes the SS dual exhaust. It's going to be close (I haven't hung the exhaust yet), but I think we'll make it. The stock single exhaust is no problem.

Carl Fausett

I can answer that "what is the weight difference?" question now.

I pulled out our digital set-up scales and laid the two systems side-by-side.

The complete transaxle with torque tube and driveshaft was weighed.

As expected, the Corvette 6-speed trans weighed more than the Porsche 5-speed.
Also as expected, the Corvette aluminum driveshaft and torque tube weighed less.

The difference between the two? 10 pounds. Or 1.1%

DKWalser

Wow! Only a 10 lbs difference? I would have thought it would have been much more than that. I imagine that the total difference (when all the other components are added or subtracted), may be more than 10 pounds -- but anything in that ballpark is surprising.

Mongo

Woah. That is really surprising.

IcemanG17

WOW...only 10 lbs.....I have a C6 Z06 torque tube in my garage right now...its not very heavy at all....but I think the C6 is heavier than the C5?

TexasDude74

All the C6 stuff is a little heavier but a lot stronger. The differential in particular is a huge improvement over the C5. The C5 diff is considered "junk" in the vette world, but that reputation comes from their tendency to explode at the drag strip. Few 928's ever see drag strips and fewer still have enough power to scatter a stock C5 diff, but if need be there are relatively cheap upgrades available. The biggest issue with a C6 driveline in a 928 is size, everything is bigger and will require more persuading. A 928 that was originally an automatic would accommodate a C6 swap easier.

Mongo

And would the swap be both c6 auto and manual drivelines?

Carl Fausett

Texas Dude is correct. The C6 trans and TT are significantly larger physically and would require hammering and modification of the 928 belly pan to make room. We thought most of our customers would not go for that.

So we chose the C5 system - it fits with no hammer involved. No denting. They are also more common and less expensive to buy.

And after-market upgrades to any C5 setup to carry it through 1000 HP are plentiful. There is no reason to fear a C5 trans and TT. Like he said, there are very few 928's who could produce enough HP and Torque to damage a C5 transaxle. But like I said, for those guys (like me) that need them, even stronger internals are available.

xschop

Good work, but I'm still at a loss why you went this direction with a custom torque tube. Are you going to have the input shaft 1x23 spline?

Carl Fausett

Yes. The custom splined driveshaft nose section will be in my hands in about two weeks and I can post a picture.

I went this way because I have a lot of customers who run one of our 3 different upgraded clutch packs. I would hate to tell them that their previous investment in a clutch is now worthless, and they must now buy a Chevy clutch and throwout package. That also raises the final price for the consumer.

My thought was, if they can use the clutch they have now, the flywheel they have now, the throwout bearing and fork they have now, the bell housing they have now - not only is their final installed price lower, but the installation is easier.

So... my drive shaft segment is "Chevy" on one end, and "Porsche" on the clutch end.

In this way, I am also able to retain the sliding coupling so that the clutch can be serviced without removal of the engine or transmission. That's a nice feature, and I am trying to keep it.

dr bob

I kinda miss seeing a leaf spring with the Corvette gearbox. I'm sure you tried to incorporate a least a piece of one in the tie bracket connecting the two rear suspension ties. Right?





Nice work all the way through, by the way.

Carl Fausett

I think the leaf spring you are referring to is transverse, and part of the Corvette rear suspension on certain models. It is not part of the transaxle mount.
We are using the complete 928 rear suspension, so we have no need for a transverse leaf spring.

Our goal with our cross-member is to replicate the strength and stiffness of the 928 cross-member before we sectioned it.
The 928 cross-member is solid and has no "spring" feature. As a result, neither does ours.

Carl Fausett

The Chevy-to-Porsche stub shaft is complete, picture attached.

This allows us to not only keep the Porsche clutch, throwout, and master/slave system, but also allows us to keep the sliding collar that makes servicing the clutch possible without removing the engine or the trans. It will make installation of the kit much easier for the same reason.

The stock part from Porsche was made from 1144 alloy, a very good material given the length of the shaft. But we thought for our application (aluminum driveshaft up to this stub shaft) we could do better and we are making them out of 9310 alloy, and then carbon hardening them to 58-62 Rockwell 0.15" deep. These improvements were recommended by the driveline engineers and I agreed.

Next (and last) piece - having the Corvette aluminum driveshaft shortened and re-balanced.