Thanks for your replies guys.

Interesting reading. I was heavily involved in the 400 scene a few years back and actually saw BDK's 90bhp FZR being run on their dyno and the resultant dyno graph on the screen, impressive to say the least! I've also seen that motor in bits and it isn't a big bore, trust me.

One interesting thing though is the amount of work they had to do to get it there, even the crankcases had to be modified as they weren't strong enough to hold together properly with that horsepower going through them, the motor has to be pulled apart after a weekends racing if it is wanted to be kept up to 90bhp otherwise it tails off to mid to late 80's but apparently it is reliable if left untouched, it just looses the edge, bit like a two stroke i guess.

I think in the end though horsepower figures don't mean that much, its what happens on track and i think everybody knows that.

As for people with 400 big bores, that is just cheating and it does go on but i can guarantee BDK don't do it, they have had loads of motors pulled apart over the years at race meetings by officials and none of their motors have ever been found to be illegal.