LSD can't do doughnuts?
 

Hey guys, I bought an 86 and the guy claimed he was told it had a torsen differential. but i was unsure and havn't personally looked into it. I know it has some form of LSD tho cause it will lay a nice even two wheeled patches when launching. But when I'm turning sharply trying to swing the back end around all the power will go to the wrong wheel, and it just spins. i can't do doughnuts! My question is, it this a sign of a weak or slipping LSD, or is this just a characteristic of a torsen diff?

its got a coilover setup, so the back end stays relitively flat. Kinda stumped with this one!

If it's a torsen, then what you describe makes perfect sense - a torsen behaves like an open diff if one of the tires becomes unloaded or off the ground. I have coilovers and very stiff springs, and I still have that problem in tight/hard cornering in autocross - although I can still do a donut pretty easily, at least on street tires - they don't produce enough grip to seriously unload the inside rear.

after reading how Torsens work, I have a hard time understanding whats happening. from what i read it seems like the slower moving wheel, with traction will get the higher ratio of torque transfered to it? i would think this would make for easy doughnuts.


correct me if my understanding is backwards

Torsens will redistibute torque to the wheel with more traction, up to the diff's torque bias ratio - eg., 3:1 would mean up to 75% of torque will be fed to the slower moving wheel, - in tight cornering (a donut?), the inside is the slower moving wheel, up until the point it lifts, or is sufficiently unloaded, at which point the diff works like an open diff and simply allows the unloaded wheel to spin. Light brake, or parking brake application can supply some brake torque to ensure the inside remains loaded and prevent the open diff effect. So a torsen has some limitations. In it's favour, they are very progressive, unlike clutch types, which when they engage and lock, can cause quick transition to understeer as the rear torque distribution is locked and the car wants to carry on straight. And unlike viscous LSDs, they wear well, making them good for OEM applications. Clutch-type lsds also wear out, but can be relatively easily rebuilt.