Re: new S4 has rear biased torque split!

["Yoon-Suk RAH" <vwaudi@nuri.net>]

-----¿øº» ¸Þ½ÃÁö-----
º¸³½ »ç¶÷: eliot <eliot@eskimo.com>
¹Þ´Â »ç¶÷: quattro mailing list <quattro@coimbra.ans.net>
ÂüÁ¶: northwest audi enthusiasts <audi-nw@u.washington.edu>
³¯Â¥: 1997³â 12¿ù 4ÀÏ ¸ñ¿äÀÏ ¿ÀÈÄ 3:48
Á¦¸ñ: new S4 has rear biased torque split!


>
>perhaps the various magazines have been too enchanted by the new S4's
>massive torque output to mention that for the very first time since 1980 a
>regular production quattro has a rear biased torque split of 46:54.
>(according to the current issue of performance car magazine, which has an
>excellent technical write up on the S4)
>
>the competition cars have been using rear biased splits for a long time
>but it took until now for us to see it on a road car.  it must have been
>motivated by the huge output of the engine.  i guess with a slight
>biasing to the rear powerslides are now more possible than before.
>
>the other less noteworthy development is that with quattro IV (i.e.
>quattro w/ 4WTC) the torsen's teeth has been blunted somewhat.
>
>old torsens had the gears cut such that torque splits of 78:22 were
>available.  the torsens on the new cars have a less agressive 70:30
>maximum variation.  i'd be interested in seeing how they use a torsen
>to do a rear biased split on the S4 since the torsen usually splits
>things 50-50 nominally.
>
>i guess that would also open up new aftermarket possibilities for hot rod
>1.8Ts too i suppose.
>
>
>eliot
>
>
>

I'v heard the ratio of torsen's distribution is up to its strength.

When I manage the Quattro Experience in Korea, Jan of 1995, I made a
question to staff from germany that why only the A8 4.2 used multi plate
type center differential(At that time, A8 4.2 used almost same center
differential as that of V8. But, from MY 1997,  A8 4.2Q also has being used
TORSEN center differential.). His reply was "TORSEN cannot stand more than
250hp.".

Then, why does the 4.2Q use TORSEN again? Because it stand 300+hp now. What
does make that possible? The "Locking ratio" makes it possible. What is
"Locking ratio"? Locking ratio means the ratio of between the forces needed
for the worm gear to rotate the worm and vice versa. That is, the Locking
ration judges the power distribution ratio of TORSEN differential.

As eliot said, most of TORSEN differential in Audi Quattros can distribute
the engine power up to 78:22. That means the locking ration is 3.5:1. But,
in case of 4.2Q, its locking ratio is about 2.9:1. So its distribution ratio
is 65:35. Why is the distribution ratio reduced? As I told before, it is
because of the reliability. The bigger the ratio, the more stress on the
teeth of worm & worm gear. So, Audi cannot help without reducing the
distribution performance for the reliability. So, the distribution ratio of
S4 is the almost midpoint between ordinary Quattros and 4.2Q.

And, S4's rearward bias of power is - as far as I think - in order to
enhance the traction when acceleration. Because S4 has so much torque
comparing with its tire width and vehicle weight, its front tires may lose
grip when hard acceleration. In this case, center differential should WORK
to re-distribute engine touque. It must be a hard work for the TORSEN
differential, as we can see in the owner's manual, "if front & rear tires
have different radius, the TORSEN differential may damage or worn
prematually.". We can see the frt-rr torque bias in the lengendary Porsche
959, its distribution range is from 20:80 to 40:60.

If sombody in list know exact reasont for that, please let me know. I'll be
happy.

Thanks.

Yoon-Suk RAH
'90 Audi 100TQ MC 220k km - custom made overboost.
SOUTH KOREA