Imagine a world where you couldn’t simply add more power to improve performance. You were stuck with what you have. What could you do to make your vehicle quicker? Higher grip tires and a suspension that keeps your tire planted to the ground will help, but the addition of the right aftermarket LSD will make your car quicker in both a straight line and around the corners without the cost and maintenance required with the former options. In fact, you may get down the quarter-mile a half-second quicker or around your local road course two-seconds quicker by simply upgrading the driven differential. While a factory LSD is better than an open differential, rarely will it compare to the performance potential from a well-designed aftermarket LSD.
By Michael FerraraDSPORT Issue #193
Aftermarket LSDs are available for the front, rear and center (AWD only) differentials of most popular performance vehicles.
Open vs. Factory LSD vs. Aftermarket
Let’s say you ended up with a vehicle that has an open differential, but the factory offered a limited-slip differential as an upgrade. Not everyone has deep pockets, so it’s only natural to consider locating a factory LSD for your vehicle. While you may find a “good” deal that makes sense for this upgrade, saving up for an aftermarket LSD is almost always the better value. While OEM LSDs have the same function as aftermarket LSDs, they are designed with stock power outputs in mind. As a result, the construction of OEM differentials is in many cases significantly weaker than aftermarket models. These differences can often be seen in the number of spider gears or the number and size of the clutch plates used within the OEM LSD. The bottom line is that if you are planning to make more than stock-level horsepower, the additional cost of an an aftermarket LSD is more than justified.
Clutch, Gear, Cone & Viscous
The LSD was born from motorsports in the 1930s. Currently, there are four classes of design for an automotive limited-slip or torque-biasing differential. To simplify the discussion, we can eliminate cone and viscous LSDs as they are not available from the performance aftermarket for import performance vehicles (cone-type from Auburn are available for some domestic applications, but no one to our knowledge offers a viscous LSD in the aftermarket). That leaves clutch-type LSDs and gear-type automatic-torque-biasing (ATB) differentials.
FWD vehicles will rarely have a drive wheel come off the ground as the weight is so biased over the front. However, if the rear wheel was to come off the ground on a RWD vehicle, most gear-type (Wavetrac excluded) would not transfer any torque to the wheel in contact with the ground.