For a 93 rx7 I heard the rear ends arent really that strong dont know how true that is but was wondering is there a stock replacement upgrade like from another car? Or what other alternatives do I have.

 

Who told you that? Probably some **** who thinks dropping the clutch at 4k rpm with drag slicks on the street is cool. The FD wasn't designed to be a drag car and IMO the diffs are generally pretty robust. A lot of guys are putting impressive wheel hp thru them. And don't forget, they're almost all 20+ years old and with six-figures of mileage on them.

For really big torque and drag racing there are braces you can buy that will help keep things together......
Differential Brace
Transmission Brace
And a diff girdle......
https://www.rx7club.com/3rd-generati...banzai-710496/

Haven't checked in a while, but IIRC there was also an aftermarket supplier of rear crossmembers that would take a Cobra differential.

 

The spider gears in the Torsen lsd are the weak point, this is why people upgrade the lsd unit to a clutch style. ATS makes the best lsd units that I have found, I run the carbon in my 20b, it is completely silent, none of the popping/clunking associated with other clutch style LSD units.

ATS LSD (93+ RX-7)