New convert under way

It's actually 5.5" O.D.
What year is your car and what is the tunnel width?
And you are correct, you'll cut away some of the rear area under the useless back seat and from the measurements I've done, the trans won't hit the back of the seats either.

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So is the Porsche one too long then? How much larger is the c5 transmission vs porsche?

The C5 manual transaxle is 23.65" from TT mating face to output shaft centers.

Done the math yet?

If you have a C5 BH and 0.6" TT adapter then your drivetrain (BH/engine interface to 944/951 output shaft centers) is 83.58" ...... The C5 is 83.90"

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Thank you Xs-chop, i found those measurements on a vette sight. My car is a 78 and the tunnel is 6" and better so no tunnel rebuild reqiured. With my measurements i agree lots of room. 80 mph on the freeway and low RPMS is that not good or what. I now there is a place in the US that will build a TT to the specs needed, with all the mods required. So coil over shocks to replace the bars in the TorsionT. Now the big question is fuel tanks. Will the stock unit work or two custom units?

The only measurement that I didn't take myself was the 23.65" measurement and was told by a builder that put one in a sand rail and the pic on the Fbody site confirms it close enough. Also you can easily fab a rubber/poly mount to go between the U-channel and the bottom of the C5 transaxle near the intermediate housing as it is just a bolt-on adapter for the differential. Since you have an Early car, you will need to pull both axles and measure the end to end lengths of each as they are shorter than the 85.5's that I build.

The C5 differential I have fits without hitting the plastic tank on my 85.5 car.

I found the other drawing that shows where the Torsion tube crosses and it is about a 10" width on the T56 housing there. I still wonder where exactly the torsion bar spline inserts sit inside the tube. It would be the icing on the cake if you didn't have to cut those out....

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Doesn't Admin/Eric have a Viper transaxle in his?

The torsion bar splines are in the center of the tube. It is the center piece that is welded to the two halves that isn't completely round.

Xschop, Thank you for taking the time with the photos and stuff, this has shed some light on some issues. My complete suspension is a 90 S2, so i am hoping your axles will work. I was thinking of removing the floor complete,( back seat area) but your drawing shows not required. I have the back trunk pan of my car removed ( lots of spot welds ). from the mesurements i have taken, on my car, should only have to remove about 6" in front of the factory u cross channel and this appears to put the C5 axle centers right close to factory. Just a thought would stretching the wheel base a few inches be a bad thing? My body mods would allow this, but i dont want to mess up the balance of the car. So the poly fuel tank will work, that solves that problem.Question, what are your thoughts on the sway bar as it sits just at the bottom edge of the torsion tube. What am i missing? everything besides the sway bar appears will work nice.
How low would the u channel sit from the ground, Do you think there is any clearnce issues. Again thank you you all your imput is valued greatly, Thre will be more questions i'm sure.

PS i will take some photos on the weekend to show my thoughts.

Actually, now that I think about it, you should make the U-channel above the trans since you're cutting the back seat area out anyways. Then you can weld DOM steel tubes over to the coilover mounts and beef them up at the same time. Then the whole drivetrain will drop out easy.

Xs-chop, i was thinking the same thing over top, ground clearance does not change, could make a removeable bottom cross support to hold trans. Thank you.

Question, could you not take the same mounts from a spare torsion unit and cut and weld, reverse there sides so they point away from the TT ( same direction as there mate )and then remove the center to allow the vette trans to fit through. The way these units mount, i dont think there is any movement in the main housing, it was all internal. Isolated via the rubber bushings for vibration? is this right or wrong. I have two units sitting here and it looks like it would work well, or do a rubber bushing at the top of the u, if there is no movement in the unit, you should be able to have two seperate mount points. I guess a plit torsion tube, independent of each other. THOUGHTS ANY ONE.

As V8carrera pointed out, the inner spline seats to the T-bars are in the middle of the T-tube and they have to go, maybe you could move them outwards and get shorter T-bars. But it would be easier to make a U-channel over the top and then brace over to the shock towers. Would be cool to incorporate the mod into a track cage

Good morning all, so then there is no movement in the Torsion tube then, Xs-chop are you thinking from top of u back to each shock point? Triangle. I think you can build the u right into the cage i intend to install.I was thinking a single bushing at the top to stabalize but back bracing would be good but must be bolted in place to allow R&R of torsion unit, allready planed to beef up shock area via the cage.Coil overs to replace T-bars. I will do a drawing ( the best i can ) so you all can see and make suggestions. Thank you.

You are on the right track. Some have just ran coilovers without bracing the shock points, but you are going to add weight with the C5 trans. I would just mod up a common Poly trans mount to the U-channel.

Thank you Xschop, any idea of the wieght diff. Is there tabs or areas where a mount can be fastened to the top of the trans. I am shopping around for a unit as we speak.

There are 2 large bolts that can be swapped out for longer ones at the top of the trans and a bracket can easily be fabbed.

Thank you Xschop, any idea of c5 weight?

I want to say 80-90 lbs heavier than ours. That would actually put me back to 50/50 weight dist.

Thanks again, weight balance very important, will keep you posted.

I had this photo on my work flash drive..... As you can see there are many points to triangulate from and the gear selector sensor housing has two large bolts that can be extended as well to fit an adapter plate for the over-the-top U-channel...

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Again thank you Xschop, i see what you mean, should be a good solid mount point to hang from, thought, would it make a big diff if i was to stretch the wheel base back 2"? this would help with my wide body conversion.

Here again the C5 trans comes thru as I believe they use 930 CV's. Cfgoija is looking into an outer drive flange conversion for our cars and that would be the key to a simpler axle swap anyways.