High Comp piston

[Warrioreater400ex]

aight guys, i want more power, but i dont want to go big bore yet or anything crazy cuz i dont have enough $$$ yet, would i gain much power or speed if i kept stock bore and went with higher compression? also would it affect my reliability? and how high could i go without havin to use race gas?

[VegasEx'r]

You can go up to 10.8:1 & still use pump gas. The higher CR will get you more power, but you might want to save up & get a cam at the same time. Also, if you are going to do the work yourself, call Terry @ Marcum's. I think he charges $15 to bore the cylinder when you buy the piston from him. That way you could get a 416 if you wanted. Whether you bore it, or go to a 10.8 CR, you won't have any problems w/ reliability.

[Leo]

I just finished putting a stock bore 10.5:1 JE piston, and XR400 camshaft in mine, along with an aluminum airbox (no lid) and an FMF PC IV-Q slip-on..

I couldn't be happier, after getting the jetting dialed in yesterday it's like a brand new machine.. Still has a nice wide, easy to ride powerband, but with a lot more low and mid range power.. Good top end gains also, but low-mid is where it really shines..

I'm loving it right now ;) I did have some slight pinging at 1/2 throttle, but raising the needle took care of that..

Leo

[Tommy 17]

i know a guy that just built a stock bore 10.8:1 je piston, xr400 cam, ported, stock carb mod, and stock mod pipe... and i guess it really is a nice set up... i haven't rode the quad yet but my friend did that rode mine and he said it was a little less power then mine but still a nice increase... way better then stock...