need help with Diff. intercgange
 

OK, I have a GSL-SE rear axle and was thinking about buying a spare diff. from a S5 GXL, does anybody know if the differential (not including the diff housing and R&P) will fit?

I forgot to ask, is an S5 GXL Diff. a Torsen or a clutch style locker?

S5 GXL is open, the S4 GXL is what you are after, it is a clutch style LSD. Only the differential will fit your 1st gen. housing, the 2nd gen pinion gear is longer making the ring and pinion useless for your application.

So are all S5 GXL's are open diff? the car is an Auto if that makes any differance. I thought the GXL was the top level NA, I mean they bothered to put 4 piston calipers on them but not a LSD?

Auto or manual, it doesn't matter. I'm not sure why Mazda dropped the LSD in the S5 cars. As far as 2nd gen N/A cars, the only ones to come with LSD were the 86-88 GXL and the 89-90 GTUs. Note, not GTU but GTUs. The GXL diff is a clutch type and the GTUs is a viscous type.

The 88 GTU also has an LSD. It was basically a revamp of the 86-87 sport, but with a LSD, TII seats, and a fiberglass spoiler instead of the rubber duckbill.

Yup, from the FC FAQ:

Turbo model diffs are bigger, and don't fit, so they don't count.

You can also use the Torsen LSD from a 1.8L miata. it's the same size as the N/A FC Diffs