[jbrucebmw]

The M differential is actually a variable rate locking differential (0-25% by many diff builder accounts). Its a fine solution and has some benefits but its not to everyone's taste. Many racers actually replace it with a traditional set locking ratio diff. I actually prefer the feel of the older style 25% all the time locking diffs in E36 and E30 because you don't have to wait for them to load up and lock. My E90 M3 often has a split second of time before the diff locks up. That said, either solution is worlds better than an open diff. I'm pretty sure the M performance set up with be a traditional clutch type diff.