I was wondering how much off a difference does ct's 310 kit make I am justr going to be racing mx with it so how much off a HP difference is there. I already have a wiseco .020 piston,boyeson reeds,uni filter,FMF gold series fatty pipe power core 2 silencer and it is ported

 

There is a huge difference between a 250 and a 310. The 310 provides a large gain power over the entire powerband, especially in the low end. It'll grunt like a 4-stroke. I own both a 250 and a 310, and the 250 can't touch the 310. For motocross racing, it might be too much, especially if you're realitvely new at it. If that's the case, you'd be better off spending your money making the quad handle better. If you can't put the power to the ground, it doesn't do any good.