Some drawbacks to the Torsen include its higher price point relative to conventional limited slips, and its cast-iron case, which can crack under high shock loads that may occur during drag racing. Schwynoch pointed out something else about the Torsen, which only appears as the result of a poor suspension setup.

"If one drive wheel becomes completely unloaded (in the air), it will spin freely," he says. "The Torsen can't bias the axle torque in this situation. This should never be a problem with a vehicle that is designed to be driven on asphalt. If your Mustang is pulling the rear inside tire off the ground, you have something wrong with your suspension setup."

The T-2 Torsen was originally designed for C-clip axle applications, and Reider Racing now carries the T-2R or Racemaster version. The difference between these units is in the maximum TBR (torque bias ratio) they can deliver. TBR is the maximum ratio of axle torque 1 to axle torque 2 that the differential can deliver.

Schwynoch explains, "If the vehicle accel-erates in a straight line, both tires can accept the same amount of torque before either one spins. If the vehicle is turning left with a lateral acceleration of 1g, there may be 400 pounds of weight transfer from the left rear tire to the right rear tire. If the vehicle started with a static weight of 750 pounds on each rear tire, the left rear now has 350 pounds on it and the right rear has 1,150 pounds on it.

This means the left rear tire can take approximately 30 percent of the drive torque that the right rear tire can take before spinning (350/1,150=30 percent). The TBR that you need the differential to deliver is the ratio of the weights on each tire. In this case, we need a differential that has a maximum TBR of 1,150/350=3.3. If the differential in the vehicle has a TBR of 2.5, then under these conditions too much torque will go to the left tire, and it will spin.

In general, the higher the lateral weight transfer of the vehicle the Torsen is used in, the higher the TBR needs to be to keep from spinning the inside tire. Street driving has the lowest cornering forces, thus the lowest lateral weight transfer. Autocross has the highest cornering forces, with the highest lateral weight transfer, while road racing falls somewhere in the middle. The T-2 has a TBR of 2.5, while the T-2R has a TBR of 4.5. In most multipurpose vehicles we recommend a T-2R. For pure street driving, a T-2 will work fine.

The higher TBR of the Torsen T-2R will prevent the inside rear tire from spinning in high lateral weight transfer situations. We have not seen any appreciable downside to using the T-2R instead of the standard T-2, while there certainly is a downside to using the T-2 in some situations."

Having now given you a short dissertation on the Torsen T-2R differential, we must say installation was a snap, at least for HP's Sean Story who had our 8.8 assembly ready for action in about an hour. The Reider Racing installation parts certainly made it easier, and it was nice to call up one place and be able to order everything we needed.