I trying to find out if there is a noticeable difference between a s4 t2 diff and a s5 t2 diff.
Are the lengths of the diff ls different?
Are the bolt patterns different?

I found two diffs local to me and I have a s4 drive shaft so I need to know if theres a difference between the s4 and s5 t2 diffs.

Also how exactly can I tell if its even a turbo 2 diff?
Are there distinct castings that makes it obvious?

 

11 ribs on the rear of the casing,as opposed to 7.
That distinguishes it from a N/A diff.
one type is clutch type the other viscous( look up that)
The s4 and Turbo s5 diffs use the same driveshaft flange so you can use either diff on whatever TII driveshaft.

 

Heres a pic of one.<a href=http://s970.photobucket.com/albums/ae182/88rota/?action=view&current=IMAG0269.jpg target=_blank><img src=http://i970.photobucket.com/albums/ae182/88rota/IMAG0269.jpg border=0 alt=></a>

 

turbo to turbo are interchangable but it must have the shafts in the diff. (all 3 types of LSD differentials use specific stub shafts)

viscous are fine but take time to lock versus the clutch type S4 which always applies positive pressure to both wheels. the viscous tend to explode in highly modified cars but i have tested them up to 500whp and not had any problems.

 

The only thing you have to worry about is that early S4s TIIs (early 87s) have different longer stub shafts and use different (shorter) axles.

other than that, S4s are clutch type, S5s are viscous.

 

Ok good stuff. I guess I would have to open the diff to tell the difference between the 2.

 

you can just pull a stub shaft and it'll tell you what it is.