I race a Cobra Replica producing around 700HP, and have a 9 inch rear end converted to independent suspension (ie no longer live axle). When I first raced the car it had a spool, which eventually let go by dropping the crown wheel off (at low speed thankfully). To get the unit apart, we had to cut the spool apart to save the axles, as the axles had twisted solid into the spool, or in fact the spool had twisted onto the axles. I guess this may relate to the breaking comments by other members about spools?
When rebuilding, I decided on trying a limited slip differential. I am not sure if this type is what you Americans call a Locker, but it is not an immediate lock, rather it uses clutches. I was advised that this may overheat and burn clutches, so I use a fully-
synthetic oil, and so far it has survived. I have also installed fittings to allow the use of a cooler, but havnt installed the cooler yet.
As for the best result for racing, very little difference, i think that the limited-slip unit has been smoother, it still always spins both wheels, so definately isnt slowing me down due to one-wheel spinning. On the street, and pushing the car around the garage, the spool was harder to move, whereas the limited slip has a little give.
I hope that helps
Cheers
Bevan Wright
Wellington - New Zealand