[s-cars] torsen rear diff; first impressions

[Mark Strangways]

Nice read Keith..
What is better, the "hacked" diff lock button of a locker, or a torsen LSD
rear.

I straight line traction I have to believe that the locker would be better.
Until there was a need to turn.
I have not yet disabled the speed drop out hindrance of my locker. I may
never, as it doesn't seem to be something that I really need. I suppose it
would help to initiate some nice fun parking lot donuts with all 4 wheels
spinning.
BTW, I have gotten it down to such an art that I can almost pivot the car on
the front / middle with all 4 wheels spinning...
Then a cop comes by :-)

Anyways, I look forward to your response between the two above, as I may be
looking for a torsen locker.
They are from an A8 ? What year ranges ?

Thanks

Mark S
----- Original Message ----- 
From: "Keith Maddock" <keith-list at maddock.uzipp.com>
To: <kirby.a.smith at verizon.net>
Cc: <s-car-list at audifans.com>
Sent: Monday, January 19, 2004 3:56 AM
Subject: Re: [s-cars] torsen rear diff; first impressions


> Kirby wrote:
> >I had a torsen rear diff installed last week.  I obtained it from Bob
> >Pastore who recently informed the list that he had a new shipment.  I
> >believe these were acquired in Germany by Keith Maddock and come from
> >V8s.
>
> Yup.  And there *might* be chance for a last batch before I leave Germany
> this summer, if enough people let Bob know they'd be interested.
>
> >Normally in slippery conditions with open diffs at each end of the car
> >and a torsen at the center, one tire at each end of the car will receive
> >power.
>
> Ack. Ack!  No!
>
> Open differentials always apply equal amounts of torque to both outputs!
> Otherwise stated, both wheels on a open-diff equipped axle always receive
> the same amount of torque.   This means that both wheels can only receive
> as much torque as the wheel with the least traction.
>
> So even  if you have a triple open-diff AWD setup, you are still sending
> equal torque to all 4 wheels.    Total traction of the vehicle is then
> limited to four times the torque that the lowest-traction-wheel has.
(note
> some center open diffs are planetary types that allow a static torque
split
> other than 50/50, such as 38/62 on X5 and some GM's, however this torque
> split is fixed and not variable)
>
> With Front/Rear open diffs, and a center torsen,  each axle has the same
> torque on both wheels, but the torsen then has the ability to allow more
> torque at one axle vs. the other (up to the limit of the bias ratio).
Each
> axle is limited to receiving twice the torque that the
> lowest-traction-wheel on that axle can handle.  Total torque becomes
> limited when the lowest traction axle has less than 1/BR of the traction
of
> the highest traction axle (BR being Bias Ratio, 3.5 in our cars I
beleive!)
>
> The rear axle of the S-Car, in anything short of full-boost acceleration,
> has less weight distribution (normal force) than the front axle, therefore
> it tends to be the limiting factor in total vehicle traction.  By
> installing a torsen (in any URS, EDL equipped or not), you're increasing
> the total traction capacity of that axle, which increases total traction
> capacity of the vehicle.
>
> >   With a
> >torsen rear diff, torque is applied to both rear tires similarly to
> >their being locked, but with proportioning according to slip.  And this
> >behavior is available at all speeds.
>
> Ack again.  The Torsen LSD biases torque according to torque (traction)
> difference, not slip.  This means Torsen reacts faster and "pre-emptively"
> when compared to a clutch type  or viscous type LSD.
>
> >Anyway, I had noticed before this transplant that I could get a rear
> >tire to slip under various conditions.  Last night I followed a newish
> >(and very clean) Corvette into Derry.  It seemed to have its wide wheels
> >on (?!) and was tiptoeing thru town more than would normally be required
> >by pedestrian risk and police supervision.  At a light where he was
> >intending to turn left I took the r.h. lane.  When the light changed I
> >accelerated at a level that he presumably could beat in dry conditions,
> >but surely knew he couldn't manage on the snow.  Obviously we weren't
> >racing as he was going a different way.  However, for me, besides
> >demonstrating to him the vast superiority of a quattro in the snow, I
> >wanted to check out wheel slip.  I didn't detect any.  Perhaps in dry
> >conditions I could have put more power to the pavement, but I was
> >impressed.  Little steering correction was needed.
>
> Good to hear that feedback, I'm really looking forward to having my own
> Torsen rear diff installed in my S4 (along with a 6-speed + LWFW + Spec
> ?*!? clutch) this spring.
>
> Nice also to hear that a bit of dirty (quite literally) work on my current
> side of the ocean has been worth it!
>
>
> Cheers,
> Keith
>
> keith at maddock.com    http://keith.maddock.com/
>
> 93 S4 (mit RS2 + BR upgrades) Portland OR
> 95 968CS (Ring Tool + Daily Driver) Koblenz, DE
> 1/8 89 GTI  16V (Spare Ring Toy)  Nürburg, DE
>
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