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    Thread: Center Differential Upgrades for B5 rallycross car

    1. 03-17-2012 09:48 PM #1
      I am looking for center and rear differential updates for the Audi quattro system in my 2001 A4.
      I race the car in SCCA rallycross competition and having just a torsen center differential is a disadvantage in low grip ice/snow events. Typically the car swaps from severe understeer to severe oversteer and back and forth with the torsen just spinning one end like crazy.

      I noticed in 2010 there were some updates to the center differential

      A new " With the new "Crown Gear" center differential, up to 70% of the torque can be applied to the front wheels while up to 85% can be applied to the rear wheels if necessary. The net result of this advance in quattro is the ability of the vehicle electronics to fully manage the vehicle dynamics in all traction situations, whether in cornering, acceleration or braking or in any combination of these."

      I have run with locked differentials in the coupe quattro's and the understeer was pretty bad. Rather than go to a locking differential I was thinking this might be an option.

      Does anyone have any details if this swap is possible? Does the new center diff require a controller? like a haldex unit?

      Would this diff, or complete trans fit in a B5 A4? would the ratio's match my existing rear end- or could I swap the whole driver train in? I haven't really kept up to speed on the new audi's so I am not sure what is compatible anymore.

      As far as the rear diff - I have machined a "phantom grip" diff insert with die springs to add 400 lbs preload to the spider gears, but it's far from a real lsd. are there any affordable options out there? OEM swaps?

      PS - my co driver and I kick the crap out of the subaru's in awd modified class !!!!

    2. Member
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      04-02-2012 09:53 AM #2
      Stasis high bias diffs. click on learn more at the bottom.http://www.stasisengineering.com/pro...late-1996-2001

    3. Senior Member TBT-Syncro's Avatar
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      04-03-2012 01:16 AM #3
      Quote Originally Posted by boost is better View Post
      Stasis high bias diffs. click on learn more at the bottom.http://www.stasisengineering.com/pro...late-1996-2001
      i dont believe the OP is looking for a center diff, but is looking for an actual rear-end differential.

      does Quaife or Peloquin have any options?

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      04-03-2012 09:40 AM #4
      He asked for center and rear here is a link to for quaife rear. http://www.quaife.co.uk/shop/products/qdf4q-0 also there is a rear lsd option http://www.034motorsport.com/chassis...i-p-17562.html

    5. 04-06-2012 10:44 AM #5
      thanks for the info guys. The stasis rear diff is way out of the budget. 2700 is just nuts for the type of racing I am running in.

      The center diff looks like a stock oe diff that they change out the teflon coated washers for carbon steel washers and a higher bias ratio. If I am wrong please correct me.

      I can see how a higher bias ratio would be good for pavement, but for the mud/ice i am looking for something with more of a locking feature, clutches. A high bias ratio wont help if ice = no grip in the rear. 0 x 10 = zero so its not going to help much.

      I am most interested in learning if the newer a4 trans/rear has any benefits and if it can be swapped into the older cars. I can get junkyard trans/diff for half the price of the stasis setup.

    6. Member o2bad455's Avatar
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      09-09-2016 10:48 AM #6
      I have some first hand experience with the Quattro system in road racing on both pavement and ice. If TorSen center (and increased biasing ratio such as 4:1 only made it more abrupt), the worst results came with matched front and rear (whether both open or both limited-slip) as the center TorSen was too unpredictable as to front vs rear bias even in the same corner on different laps. That said, there are things you can do to force bias towards one end or the other (think forcing one end to lose grip first), but they are all a bit slower since the goal is generally to retain grip. I always wanted to build a 6-speed transaxle with lockable center diff as in the older Gen 1 cars but with TorSen in unlocked position for testing purposes, but never did get around to it. Perhaps a later ('08-up) rear-biased center diff would help, but probably never as much as just locking it.

      For pavement (suspect this might be driver and suspension dependent), best combo seemed to be locked center diff, limited-slip rear, open front. Torque-biasing (TBD) rear (e.g., TorSen from an early 90's Audi "V8" - NOT A8) was almost as good in the dry (and perhaps better in the wet), but our early-production unit (with semi-open casing) failed early on a hot day (a diff cooler might have helped). Limited slip front actually hurt laptimes in dry and even worse in wet, but torque-biasing front with limited-slip rear might be the bees knees.

      For unstudded ice, torque-biasing front (well worth it if in budget), locked center, and torque-biasing rear work best (keeping in mind okay to match front and rear types as long as no TBD in the center position. On a tighter budget, lockable rear (see below) with the stock TorSen Center, or Torsen rear with a welded center both work well. Locked center and rear were a bit too much, though, as force too much slip between front and rear. For race-studded ice (e.g., Menards), any of those or even the pavement setups work fine.

      Here's some low-budget interchange info that I've compiled (please LMK if any errors noticed):

      Audi B5 A4/S4 Quattro (USA):
      01H500040J 35:9 DAJ (100mm CVs) Probably all A4 5-Speed
      01H500040K 37:9 DAK (100mm CVs) Probably all A4 Tiptronic
      01H500040L 37:9 DQA (108mm CVs) Probably all S4 6-Speed (ratio same as A4 Tip)
      01H500040N 35:9 DXT (108mm CVs) Probably all S4 Tiptronic

      Audi B4 93-95 Audi 90 Quattro (USA):
      01H500040D 35:9 CAV (100mm CVs) with Diff Lock

      Audi B4 93-96 Audi 80/90 Q (Germany)
      01H500040D 35:9 CAV with Diff Lock
      01H500040 37:9 AZC with Diff Lock
      01H500040B 37:9 AZE with Diff Lock
      01H500040H 41:9 CMB with Diff Lock

      Audi "V8" (37:9 for at least the 6-Speed, but R&P won't work in B5 housing anyway):
      AFV Auto with TORSEN
      AXZ Manual with TORSEN

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