Just curious, what kind of upgrads can be done to a S3 GSL rear end? I know you can put a TorSen diff in, but what else can you do? Bigger axles? If so where can you get em? Anything else?

 

You can use the Torsen off the S or Touring type Miatas. I was told these only have beige interiors, however I am not sure how else to tell if the car is in the scrapper... Maybe VIN decode.

You can swap ring/pinions out of several cars...

Miata, B-Series pickup (4x4 Front diff only), Kia Sportage

I forget whether MazdaTrix or RX-7.com has upgraded strength axles... One of them does because they were breaking during the racing season. I know it's one of the two...

Guru Motorsports of Australia has a floating axle kit that makes changing alxe shafts easier.

I tink that's about it. It's supposedly a pretty nice solid rear end for N/A rotary applications.

EDIT: Note that the S3 has larger axle shafts than the S2 or S1. Although the driveshaft yoke is smaller, I think...