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Re: Torsen Test

Here's my $.02 worth on the subject:

1) Audi wouldn't have switched to the Torsen diff if it weren't superior to
the old setup.  The latest system, quattro 4, uses the Torsen diff with EDL
on all four wheels and is fully automatic.  Now you can get going even if
only one front wheel has traction.  Also, EDL operates up to 25 MPH (manual
lock on quattro 2 cars has auto disengage at 15 MPH) and ABS remains
operational.  This seems like progress to me.

2) Torsen diff allows CONSTANTLY VARIABLE torque split between two outputs.
 With quattro this is UP TO 3:1.  From what I understand, a Torsen diff has
the amazing ability to proportion torque before tires actually loose traction
and start to spin.  In a quattro this proportioning even occurs when going up
or down a hill on dry pavement!  Also, FWIW, I have read in many auto rags
that Torsen diffs are the ultimate.  With a viscous coupled AWD design
(Subaru, etc.), one output shaft has to start spinning significantly faster
(read tires have lost traction and started to spin) than the other to trigger
viscosity change and subsequent locking.  Other problems with VC systems:
high torque input required for diff to actually start locking and under heavy
use diff fluid can overheat and not function properly.  These systems are
also usually biased to send 65-100% of torque to the front wheels under
normal conditions and may only achieve a 50/50 split under full locking.

3) Personal experience.  I tested the Torsen diff this way:  I found a
perfect patch of ice in a parking lot and drove up to it,  placing the front
tires on the ice while leaving the back on dry pavement.  From a dead stop I
engaged 1st, revved the engine, then quickly released the clutch.  The front
tires spun on the ice (still getting 25% of high power output), but the car
*quickly* accelerated forward as if there were no ice.  This is b/c 75% of
torque was being sent to the rear wheels on dry pavement.  When the rear
tires hit the patch of ice (front was now off ice) I didn't notice any spin.
 With an open center diff the car probably would not have moved under this
scenario because all torque would be lost to front wheels spinning on ice
(certainly wouldn't get hard, controlled acceleration).  Conclusion: TORSEN

4) Do the math.  According to my calcs, the quattro 1 system will transmit
25% of torque to each rear wheel with both diffs locked.  The quattro 2
system will transmit 37.5% of torque to each rear wheel with rear diff locked
and Torsen at full rear bias.  That's a 50% increase.

5) More personal experience.  Winter of '92/'93 was brutal in Philadelphia
(more ice than I've ever seen), but my CQ never missed a step.  Best example
came one afternoon after leaving the office.  I had to go up a steep hill
that was in really bad shape.  I'm talking stuck cars everywhere.  Everyone
in front of me was turning around and people stuck on the hill were trying to
back down.  A guy rolled his window down and told me to turn around. I
responded by saying, "This is a quattro, watch this."  I then locked the rear
diff, pulled into the left lane (to get around stuck cars), and accelerated
smoothly up the hill.  People were staring at me in utter disbelief,
particularly the three SUV drivers who were also stuck!  BTW, I was on all
season tires and not using chains.  Conclusion: TORSEN WORKS!


Kennon Hines
1990 Coupe Quattro
Atlanta, GA