was wondering about this...

[MadKaw]

is the dirt bike classes in the races required to have 4-stroke, or is it a 450cc max?

if its a 450 max, could you sleeve the cylinder and put a smaller piston in the 500 to make it a 450? and if so, would they allow this into the races?

[demographic]

Some of the racing over here (In the UK) is now 450cc max which is why a bloke who built a 450/500 hybrid wasn't allowed to race it.

Well thats what the bloke who owns our local Team Green shop said anyway.

[gwcrim]

I think I read somewhere that the open class is now OPEN to all bikes.  But I may have beeen halucinating.

[Paul]

If you are refering to Super Cross type events then the answer is not really. The rule states nothing bigger than 250cc 2 stroke and somehwere in there they allow four strokes up to twice the displacement. This is a rule from way back when - when no one ran a thumper, they just didn't make enough power to be competitive. Even now at equal displacements they don't make the same power.