In a message dated 98-01-16 18:01:38 EST, you write: << What rear diff was used in the earlier version of the S4? If not the torsen, why not? If the torsen is desirable, can it be retrofitted in other audi's >> The S4's and S6's use a locakble rear diff similar to the 5000 qt. Yes the V8 rear torsen can be swapped into other Q's but I don't think it's worth it it adds to the understeer.. Scott