330 Big Bore Kit

[EXrider02]

How many of you guys are running 330 kits? And have you had any trouble with reliability at all? How much of a power and speed difference did it make?

[Scott]

I'm not running a 330, but I've ridden with many and watched many race hare scrambles over the years.

Since I don't own it, I can't comment on reliability.
Power and speed, night and day difference from stock. Close to a stock 400, and strong enough that you may want to consider an extended swingarm to help keep the front end down.

If it were mine, I think I'd check out a 305 kit first. Major improvement over the stock power. I'm not one to bore out a cylinder just because I can. I like to have as many future rebuilds as possible left in the cylinder. If I remember correctly, the 305 doesn't mean a new sleeve, but I'm not so sure about the 330. It may be a new sleeve in the jug.

Ever think about trying a stock bore, higher compression (say 10:1 or 11:1) and have the head port & polished? Assuming you've already changed the pipe and air filter, that would open up the head and let it flow better. Kinda maximizing the stock engine instead of boring it out. Maybe even hardface the rockers and swap the cam to take advantage of the port and polish.

Isn't the 300ex head actually the 250X head? Why not open it up a little?

Either way, Good luck.