I broke bc box twice in a week running zetec turbo 280 bhp 300lbs , both times stripped every tooth off the crown wheel and pinion, they were brand new ford items as well , second time it looked like they had been machined off they were that smooth lol. I drove like a twat thou. It was also fitted with a quaife diff.
Not bad really £500 in a week and a bag of bits

Cheers paul