I ride MX and need more power to run with the moded 400's. I was wandering what mods such as cam piston and bore would give me the greatest performance gain with still maintaining great reliabilty. I was at first thinking of a overbore that would get me to 426cc, but I was wandering what the other standered bores such as, .040 or .080 would give me performance wise and displacement wise. I was also thinking of a webcam and 10.5:1 compression ratio on the piston. Please any imput would be apreciated. Thanks.

Chris

 

ok,don't know about bore sizes but i can talk a little displacement. If you ride amai think you can only go to a 416 displacement if you race in the 4 stroke class, the gncc has an open class which i think you can run any size you want. i assume that you already have a pipe, silencer, cdi and filter, advanced timing key will also help. if you are gonna overbore, get a piston and cam and valve work to go along for the full package. the biggest kit is a 500. most i know ride a 416, 426, or a 440. before you go for the total haul, look into port matching and maybe a custom intake will help a lot, i got a 400ex with curtis sparks cdi, timing key, race exhaust, filter, air box screen, and reinforcing ring and it hauls flat out, but don't know how fast it really is, don't have a place big enough to top it out.

 

A couple more questions. First does any body no what the over bore is to get to 416 or 426. And Second the timming key what will that help with. I am still learning about the motor. Third and probably not final what is the difference between the Curtis Sparks CDI and the White Brothers?

Thanks

 

Come on somebody has to know what to do to a 400ex motor. Please Reply anything would be appreciated?

 

Common 400EX overbores:

Stock Bore X Stroke = 85x70

86mm bore = 406cc
87mm bore = 416cc
88mm bore = 426cc
89mm bore = 435cc (sleeve req, known as a 440 kit)

 

Here's what I'm working toward:

426 big bore (done)
Uni Air Filter (done)
Curtis Sparks Pipe (On order)
Curtis Sparks timing advance key (On order)
Edelbrock Carb (On order)
Cam (don't know which one yet. Probably Sparks, LRD, or TC)

Dennis