[torsen] Spider Bites in the new milenium...

[Jeffrey Goggin]

Okay, here's the deal: I've now driven my A4 in an even dozen autocross 
events since January (6 to 8 runs each), as well as a novice driver's 
school (hey, it was seat time) where I was able to make 20 runs and 
spend an hour playing around on a skidpad, and I've yet to experience 
anything even remotely similar to the "spider bite"  phenomenon that 
caught me off-guard in my '89 200q back in 1997-1999.  There is no 
question that my A4, as presently setup, is the quickest Audi I've ever 
driven around an autocross course -- at yesterday's event, I was able to 
run times that split the Z06 Corvettes in SS! --  even if it's not yet 
as competitive in its class as I would like.  Although it doesn't (yet) 
have enough power to kick the back end out at will, on those occasions 
when the back end does break loose, the car is usually easy to control 
with a bit of opposite lock and a deft foot on the throttle.  In fact, 
yesterday, I had the back end let go several times at the fourth cone in 
a seven-cone, top-of-second-gear slalom and despite having the car luch 
from opposite lock in one direction to opposite lock in the other 
direction four times, I didn't hit a pylon even once and was easily able 
to bring the car back under control after it scrubbed off a bit of speed 
and the course didn't require me to keep the car turning...

I'm told (but haven't yet confirmed) that Audi reduced the Torsen's bias 
ratio from 3:1 (Type 44, B4) to 2:1 for the B5 chassis cars.  Is this 
"softer" bias ratio the reason why I haven't experienced any "spider 
bites" with my A4?  Or was the "spider bite" a chassis problem after 
all?  Stasis Engineering offers a $550 mod for A4/S4 Torsen center diffs 
that increases the bias ratio to 4:1 (and I'm told, 5:1 is also 
available) and are racing this diff in their Speedvision cars 
semi-successfully, likewise without experiencing any "spider bites."  
Frankly, I don't know what to think now.  The theory behind the "spider 
bite" still strikes me as being sound, yet I've provoked my A4 several 
times now and it has yet to even _hint_ at biting me, let alone actually 
do so...

Which brings me to my question: With performance as my primary goal, 
should I modify the spare Torsen center diff I recently bought off eBay 
to _increase_ the bias ratio or should I have it welded up and instead 
turn it into a locked center diff?  To complicate matters further, the 
research I've done suggests the Type 016 Torsen center diff is a direct 
swap for the Type 01A's Torsen, which (if true) means I have the option 
of bolting-in a locked center diff, leaving the OEM A4's 2:1 diff alone, 
swapping a 3:1 Torsen from a Type 016 tranny (the one in my '89 200q 
comes to mind!) or modifying/having Stasis modify the OEM 2:1 diff into 
a 4:1 or even 5:1 diff.  Decisions, decisions...

Mind you, all is not well in Torsen land.  Thanks to the fact the Torsen 
center diff is a torque multiplier, when the inside rear tire lifts (as 
it has on every Audi I have ever setup for autocrossing), AWD becomes 
ZWD (zero-wheel drive), causing the car to coast through the turn until 
it slows enough the inside rear wheel drops back to the ground, the 
Torsen starts allocating torque again, and forward motion resumes.  This 
has been a major problem for me, despite EDL (which seems to react too 
slowly to be of any help), and I've spent quite a bit of time trying to 
soften the rear bar and stiffen the rear springs in order preserve the 
handling balance that otherwise seems to work so well while keeping the 
inside rear tire planted.

Fortunately, the cure's relatively straightforward: Install a 
clutch-type limited-slip in the rear diff housing.  Stasis Engineering 
sells one ($1895!) but a used 944 LSD will also fit with some minor 
die-grinder work and although they are becoming hard-to-find without a 
transmission attached, when they do turn up, they can be had for 
$5-800.  I've had one for a couple of months now, but haven't managed to 
get it in the car since I have to farm it out to someone with the proper 
tools and I've not been able to coordinate my schedule with theirs.  
Quaife also offers a torque-sensing rear diff for the A4/S4 (not because 
there's any great demand for it from Audi owners, but because it also 
happens to fit the Porsche Boxster!) but since it shares the same ZWD 
characteristic of the Torsen center diff, this really doesn't solve the 
problem.  Nor would a rear Torsen from a V8, assuming it would even fit.

Anyway, there you have it.  In years past, I was one of the louder 
voices in the choir (hah!) and although I still know the lyrics, the 
sound is rather different these days.  Has anyone ever been bitten in a 
B5 chassis car?  Discuss among yourselves...