I agree with Myron (Locomotion); the efficiency is in the centering of the pinion to the ring gear. An old SS/FC racer buddy who's basically a genius at mechanical principles, also pointed all that out to me years ago. And he runs a 12-bolt conversion diff in his 9-inch housing in a 12-second stick Chevy "toy" that he races. Years back, some SS/AH cars were playing with the 12-bolt diffs, not sure what's in them currently.