hey i have a 02 400ex i want to put a big bore kit in it, but been wondering how reliable it would be. i was also wondering if anyone did this and how there quads a running. [img]i/expressions/face-icon-small-confused.gif[/img]

 

don't go over 11.1:1 comp. and it'll be fine. if you want 12.5:1 beef up the bottom end.

 

It will be fine. But if your just gonna big bore it your not gonna get the power your expecting. You need everything together. Big bore, porting, full pipe, cam, carb.
Depending how far you want to go you ccan got as far as 90+mm bores , stroking, larger valves and real hi compression 12:1 +

 

Ive had the 440 bore for over a year. A lot of my friends also have the 440 bore. The bottom end is fine in all of ours. But it wont be as usefull as the 416 if you dont get the other components. I run the 13:1 and love it, but it takes race gas. I prefer U4, but you can run any of the other 110 race gas out there. Let me know if you want any help or advice on the other components.

 

IMO go 416/426