Alright guys.

Pretty new to the rx7 community so please feel free to correct me.

I'm 99.99% sure all FD's came with a torsen LSD, but for some reason I'm just getting 1 tyre fire.

I had it up on the ramp at a friends work today to make sure I'm not being an idiot but when I spin one of the rear wheels the other just stays still (like it would on an open diff).

Any opinions on if there may be something wrong with the diff or whether someone has changed it for an open diff (not sure why anyone would).

Thanks.

 

torsen's don't wear out, so either you're seeing normal operation or someone put a TII clutch pack diff in your car and the clutches wore out. the clutch type LSD is actually more favorable for drag racing but it does require maintenance unlike the torsen. torsens will do one wheel peels under certain circumstances.

 

Torsens ARE open diffs. They are not limited slips.

They have a variable torque split, which mimics the effect of a limited slip, without the downsides of an actual limited slip. Thus, people will (incorrectly) call them "limited slips". They will quite happily allow one wheel to effortlessly spin while the other is stationary, so they don't limit slip in any way.

The "effortlessly" is the key. Bevel diffs have a fixed 1:1 torque split, while Torsens can allow a variable torque split, usually around 2.5:1 although I have seen as high as 4:1. This means if the "slipping" wheel is getting 50 ft-lb then the non-slipping wheel can get as much as 200ft-lb. (The downside of course is if the "slipping" wheel only can put down 0 ft-lb, the non slipping wheel also can only put down 0 ft-lb... 4 times 0 is still 0)