High Comp Pistons

[clutch25]

It looks like almost everybody uses either JE or wiseco high compression pistons...

Has anyone used a CP for a HC build? I've got one in my 450 and like it.

From what I remember 11:1 is right on the edge of needing race fuel correct?

I have a buddy that just had me put a HC stage 2 in his 400 and now he got a taste of some power...wants more!

I should have never let him ride my 450R with 14:1...!

Thanks

[XXXRACER165]

SWEET! Actually 12.5:1 is the limit.

[GPracer2500]

Originally posted by XXXRACER165
SWEET! Actually 12.5:1 is the limit.

?? I couldn't run 91 on my particular build with a 10.8:1 JE. Although, most folks report doing fine with 11:1 pistons and pump gas.

11:1 is commonly though of as the pump gas "limit" for the 400EX. But the "limit" isn't set in stone. The particulars of each build, local pump gas specs, and riding environment will have the final say.

[gcart2]

well it runs good on 93 and bad on 110. but if u do a 50/50 mix it runs perfect!

[clutch25]

Originally posted by GPracer2500
?? I couldn't run 91 on my particular build with a 10.8:1 JE. Although, most folks report doing fine with 11:1 pistons and pump gas.

11:1 is commonly though of as the pump gas "limit" for the 400EX. But the "limit" isn't set in stone. The particulars of each build, local pump gas specs, and riding environment will have the final say.

Thanks GP...!

We ride around 1K to 2K above sea level and in temps down to -20F. Even with the stage 2 cam, I'm guessing that it will probably be a race gas application.

Does anyone know if the CP pistons are single ring or 2??? CP seems to be the one with the highest compression and lowest overbore option.

[400exrider707]

Originally posted by clutch25
Thanks GP...!

We ride around 1K to 2K above sea level and in temps down to -20F. Even with the stage 2 cam, I'm guessing that it will probably be a race gas application.

Does anyone know if the CP pistons are single ring or 2??? CP seems to be the one with the highest compression and lowest overbore option.


What machine is this going in your EX correct? Cam selection plays a huge role in fuel requirements. Static compression means nothing, its the dynamic compression that determines fuel that needs to be used.

I think you will have quite a time trying to find a single ring piston for your EX. CP would either be three or two, most are three. Remember on the EX motor, anything over say 11:1 it is recommened you use a heavy duty rod, and heavy duty head studs. This all must be factored into build cost, if money is an issue.

[1965 honda]

Originally posted by gcart2
well it runs good on 93 and bad on 110. but if u do a 50/50 mix it runs perfect!
i run the same thing. i use torco most of the time but im tring turbo blue for the next couple of weeks.

[clutch25]

Originally posted by 400exrider707
What machine is this going in your EX correct? Cam selection plays a huge role in fuel requirements. Static compression means nothing, its the dynamic compression that determines fuel that needs to be used.

I think you will have quite a time trying to find a single ring piston for your EX. CP would either be three or two, most are three. Remember on the EX motor, anything over say 11:1 it is recommened you use a heavy duty rod, and heavy duty head studs. This all must be factored into build cost, if money is an issue.

Yes...it is going into the 400 EX. I am very aware of how cam selection effect dynamic compression, hence the reason I included the cam model in the post along with alt. and air temp to give an idea of air density that we deal with around here. I won't do any high comp piston for my buddy unless he agrees to get the cylinder studs done, I wasn't aware of the requirement for a heavy duty rod...

By a single ring, I mean compression ring, not including the oil rings. My CP for my 450r was a single ring piston and I would rather have a dual ring in the 400.