quattro digest, Vol 1 #3237 - 1 msg ->"Care to Comment" -> differential tuning

mlp mlped at qwest.net
Sun Apr 7 13:29:59 EDT 2002

Sorry Rob, I should have read your post more carefully all the way to the

So I take it Stassis Engineering does exactly that, offer "blue printed"
center differentials etc.?


~-----Original Message-----
~From: quattro-admin at audifans.com [mailto:quattro-admin at audifans.com]On
~Behalf Of quattro-request at audifans.com

~   1. Care to comment? (Rob Andrews)
~From: "Rob Andrews" <randrews at sbcglobal.net>

~From stassis engineering....
~Differential Tuning
~Tuning the center differential provides one of the most significant
~performance gains available to the Quattro owner. The standard
~torsen center
~differential in the S4 and A4 provides a 2:1 torque distribution
~This enables the end of the car with traction (generally the rear) to
~deliver twice the torque being delivered by the least tractive end of the
~vehicle (generally the front). For high performance street cars, we
~recommend a bias ratio of 4:1. This is the same bias ratio that Audi has
~provided in the stock RS4 driveline.
~In professional competition a high bias center differential provided a
~performance gain of almost 2 seconds a lap. This is the equivalent
~of adding
~60hp to an S4. This is our first step in almost every tuning project. It
~provides a measurable performance gain for track-oriented drivers. For the
~enthusiast street driver in good weather conditions, it can provide the
~balance and control of a rear wheel drive vehicle, as 80% of the cars power
~will be applied to the rear wheels upon corner exit.
~The center differential in an S4 is a slip in cartridge accessible from the
~rear of the transmission. The A4 center differential is a self-contained
~bolt on unit. Install time is approximately 2 hours.
~Center Differential rebuild A4/S4 - $500
~Rob Andrews
~99 A4 2.8QS   83 Ur-Q
In recently discussing the use of, the need for and the marketing being done
by one particular dynameters that has recently become accessible locally,
the shop manager made the comment that he was being told, something to the
effect, "All (hyperbole, probably some or many) the Winston Cup teams (i.e.
"money is no real object IF it will get us a competitive advantage) are
looking at, intererested in, or buying their own personal versions of the
particular form of dyno i.e. it's capable of measuring power, or more
importantly isolating power loss, at each individual wheel.  He said since
rules on engine displacement and air intake formulas have gotten so tight &
stringent, the teams all pretty well know how much bhp they can make their
engines make; and know they aren't going to be able to squeeze any more
ponies out of them.

So a big part of the racing team focus now is on how to make the chassis
components, particularly the gears in the transmission & differential, as
light and efficient as possible.

I suppose "differential tuning" would fall in this category.

Your comment touches on another theme / debate that turns about the use of
this dynometer in particular, and the "hard" data supplied by all chassis
dynometers in general when the bar stool crowd gets around to trying to
intelligently discuss or compare tuning results from car to car, engine to
engine etc.  And that is (a) do you know if the figures you are throwing out
are wheel power numbers; of flywheel numbers?  (b) can you tell if the
"chart" you're looking is "raw" data; or an "adjusted for:  "tcf"
(transmission correction factor, aka drive line loss aka ????); temperature
or altitude; or ????

In the quattro world I've seen an interesting range of numbers used for some
of these efforts to convert apples to oranges into an apple to apple
comparison.  They've ranged all the way from a suggested 10% adjustment on
an AWD 996 Porsche (see, for example
http://www.evoms.com/p_996tttune.html  to
25% for AWD Audi Quattro drivelines; to @ 21% for a triptronic FWD VW box
(see the March/April 2002 issues of EuroTuner for a 2 part series on a PES
1.8liter VW Jetta tuning/dyno/tuning saga.)

Anyone dealing with a machine shop who wants to offer to "blueprint" you
center diff?


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