As far as anyone can tell - they are all 3.7. The *mythical* factory 3.9 LSD hasn't shown up that I have seen. You can take the guts out and put them into any other ratio diff including 3.9, 4.111, and 4.444. It's not a hard swap.
There's one across the street from you. STIs are 3.90.
well, i just ordered a front OBX lsd so , when i go to it you are more than welcome to come over and help....cheers, b
Nice. You'll be happy with it, I'm sure.
A thread on NASIOC has a full tear down of the diff.. pretty interesting... the machining is hit or miss.
The machining on mine was acceptable, just not as shiny as the Quaife. GD and I just replaced the washers and bolts like the instructions on NABISCO said, and it seems to work fine.
The vast majority of LSD discussion here and elsewhere is *about* rear LSD's. Those come stock on many models from the mid-'80s on. All WRX's and STi's have them as well as my '91 Sport Sedan (SS) and many others including some turbo Foresters, and Outback XT's, etc. The other recent post by Zap in this section deals entirely with rear LSD's and what people have noticed about how they react depending on type.
Not all WRXs came with an LSD, actually.