[s-cars] Torsens is there a difference ??!!

[QSHIPQ at aol.com]

Thanks Rob, I'm sure you haven't visited the archives :).  First, since the
torsen is "torque sensing" it's operation is different than a clutch type or
a VC, in that for all practical purposes the torsen allows no speed
differential, it's already changing torque allocation before that happens (it
only allows speed differentiation at max TBR).  This makes it different than
a VC or clutch in that some slippage is expected and needed before a revised
torque allocation.  The infamous torsen "hunt" is it's own inherent design
problem.

Torsens at really high TBR (read:  Audi applications)  are pretty much at the
maximum of the design of the torsen unit itself.  Choosing anything over
3.2TBR isn't much more than academic, since in practice the higher you make
the initial TBR, the shorter that TBR will stay at that level.  Torsen
actually says that the 3.2TBR of the new university special is delivered at
3.2TBR, and "settles in" at about 2.5TBR.  When we get up to the 4 vs 3.5TBR,
I doubt in practice anyone could claim one over the other, including torsen
themselves.  My thinking is that the common tweeking practice of the torsen
tuners to put steel washer instead of needle bearings which tends to beef up
the internals of the unit, and as an incidental side effect, it slightly
changes the advertised TBR.  This might explain why the high torque
applications of the 6 speed (your 751 blank) 4.2v8 and RS2 carry the
different part number.  All that said, they are completely interchangeable
with the 751E, since dimensionally they are identical for the 01E trans.

So, should we have our *choice* of torsen center diffs, you'd maybe want the
751 blank, not for any TBR "advantages" (I just don't buy into that or it's
effects), but maybe for the marginal extra torque capacity.  I sure wouldn't
go out of my way to acquire one, any of the old university specials can be
beefed up with common available parts.  Personally, I'd be a bigger fan of
reducing the TBR, not increasing it in an audi chassis application.  My bet
too, is that those with big ass swaybars are going to become very familiar
with how torsens take shock loading....

HTH

Scott Justusson