I think the main difference between Posi, LSD & Mopar's "Sure grip or Sure lock is the auto maker. Ford = posi, GM = limited slip or locking & Mopar = Sure grip. Mine spin's posi till you try to bring it on around for a doughnut, when most of the weight of the car is on the outside rear tire it quits spinning. As long as I going in a fairly straight line it leave's about $20 worth on rubber on the road in two line's.