Alright, I have a 1990 535i 5-speed and I just got under the car for the first time only to see a big "S" on the bottom of the diff. I was always under the impression that it was an open diff (I think I searched what the stock 535 diff was, can't remember it though), so now I'm left wondering what ratio mine is.

At 3k rpms, I'm going 80mph in 5th gear. That's about all I can give you.

Anyone have a guess as to what it is? I'd rather not be told to get under the car and check out numbers on the side of the diff.