Quote Originally Posted by nilak View Post
IÂ’ve watched this presentation youtu.be/E0yZdLkpvR0 some while ago and these guys did some extensive research on this transmission. They say it can handle even 475lbft although itÂ’s rated by the manufacturer dor a lower torque (I think 400lbft). But taking into account itÂ’s now over 30 years old and 130k miles, I thought something like 400lbft would be better for reliability. Anyway 12% over 400lbft does seem a huge step, it could be safe.
Another problem can be the the C beam, but that basically depends on the output torque not input (engine) torque and I think can be a problem if you use drag tires even with std engine, 1&2 gears can generate enough torque up to race tires traction break up.
What I read is that the 92 and earlier ZF6's were German made and rated for 450 ft-lbs. GM licensed the design and in 1993 began making their own. They changed the design of some of the helical gears to lessen gear noise and then rating dropped to 400 ft-lbs.

I also came across a thread where corvette owners were successfully drag racing with the Dana 44 differential and laying down some low 60 ft times. Not sure is you have Dana 36 or the Dana 44 but the 44 sounds strong. I did find info that said the 1993 and later Dana 44's were somewhat stronger.

I think you are being overly paranoid about breaking stuff. Install a good clutch and drive the car. If something breaks upgrade it.