IM WANTING TO INCREASE MY TOP END SPEDD AND GET OUT OF THE HOLE BETTER. WANT TO KNOW HOW MUCH A HIGH COMPRESSION PISTON WILL HELP? ALSO ANY OTHER MODS YOU CAN THINK OF. IT ALREADY HAS STAGE FOUR EXHAUST,STAGE 1 HOTCAM, JETTTED, AND I HAD IT PORTED

 

top speed is a factor of gearing. Higher geared gives more top speed and lose sum bottom end. What are you riding man you didn't say what your riding?

 

The 400EX is bulletproof, until you start messing with the engine internals. While it did make sense 10 years ago (when it was the only 4-stroke game in town) to mod up the EX, now it makes more sense to move up to a higher performance machine, and leave the EX alone and preserve its legendary reliability.

 

OH! in the "Topic Summary" I see. Ya I agree with recon. The 400ex is the best trail sport wheeler. It's not a racer.

 

if you want high compression, je makes a great piston. from factory the 400ex is bullet proof. now i dont know about these other guys, but i have a 426 (13.5:1) on a HD hotrod crank. with a web cam. ( yeah...web) went from like a 243 or something lift, to a custom 411 lift. short guides, 3 angle job. port n polish. and dynatech cdi. never had a problem. had it like that for some years.

good luck, and hope this helps