400ex piston question

[dbo005]

i wanted to know if i ran a stock bore 11:1 high compression piston would i see any noticable gains. i have a full hmf system and k&n filter and jetted. also anyone out there that has a full hmf system that runs at above 3,000ft elevation could you give me any good jetting ideas.

[cals400ex]

i bet you won't notice too much with just the piston. however, it would be noticable if you put in a cam too. i only went up from the stock 85mm to a 86mm piston at 10.8:1 compression with a cam and there was a very very nice difference.


for jetting it matters if you are running keihin jets or dynojets. the temp plays a big role too. for keihin jets i would start with a 158 mainjet. you can always fine tune if need be.

[dbo005]

thanks i am running dynojets

[cals400ex]

i imagine you would want to go smaller then if your using dynojets. maybe a 155 or even the next size down from what i read on here.