Im in the process in rebuilding my motor & Im not wanting to put it back to stock or change the stock bore (like 440kit) yet. So I would like to have everyones opinion on what is the best higher comp piston & ratio to buy for the 400ex. Ive also thought about buying the XR cam to help out the powerband alittle. So please give me some info what you guys think is the best combo to go with. Any pries, #'s or websites to places to find the parts would also be helpful. Thanks!!

 

With the 11.1 do you have to run race gas. My bud was wanting to put a 440 kit in his and he was curious.

 

BG 400,I'm running a JE 10.5:1 stock bore with the GT Thunder cam and it's a whole different machine than what it was. I've also heard nothing but good things running the XR cam. If you want to talk to ppeople that have them go to Exriders.com.By the way,I don't have to run race gas with this piston, I have heard that anything over 11:1 you have to.I just chose to be safe and am very happy with my choice.Jim

 

Depending on what type of cam you have and how your engine is set up 11:1 is not the limit on pump gas. Most people do stop at 11:1 though just to be sure they can always run pump gas.

 

Hey BG400;

I emailed you back with some more info. I also told you am running race gas or 50/50 mix with my 11:1. My quads pings under hard load (hill climbing, cornering hard in loam or mud) when I used pump gas, I do have my head milled .015" which makes a little difference, but I think you will find that yours may ping also w/ pump gas. So 11:1 is about the breakover point where you have to run more octane than pump.

Nick

 

right now im running a JE 10.5:1 piston, TC cam, Pipe, and some porting by MP Racing, right now im betting stock banshees on stock gearing. Im going up to a JE 12:1 piston this winter for some more Comp.