[Fred44nl]

all quattro Audi's with a transversal engine, like A3, Q3, TT, don't have a torsen diff.
they have the Haldex-clutch, located just before the rear axle.

all quattro Audi's with longitudal engines, like A4, A5, A6, etc.etc. have a central torsen differential.

 

[Fred44nl]

All the f/l B8 A4/A5/Q5 don't have Torsen anymore.They have the new crown gear differential.

the pré-FL have a torsen-diff type "C".
the FL do indeed have a "crown gear" differential, which also works on the difference in torque and/or difference in speed between the front and rear outgoing axle.