13.5:1 JE piston

[allaboutHP]

is a 13.5:1 compression ratio ytoo high for 93 octane gas???

[wheeltrax]

yep

[cals400ex]

yes it is. most won't go over 11:1 on 93 octane and some won't even go that high.

[Juggalo]

WAAAY too high

[2muchquad]

actually maybe not,my yz mx bike has a 13.5 to 1 piston and i run 93 octane no problems.i would imagine it all depends on the motor.

[khen]

It definitly depends on the motor.. I've got the 416 11:1 Wisco piston with the XR head gasket and RTV in place of the base gasket and mine pings on 91 octane(highest we have here at the pump). I ride mostly at about 4500' elevation so I thought for sure I could get away with 91. :(

[cals400ex]

i have talked to people who run pump fuel on a 12.5:1 rated piston. not saying i would recommend it but i have talked to people who have. by the way, this was on a 400ex.

[TC426EX]

Dude, you run pump gas with that 13.5:1 piston and youre gonna have SERIOUS detonation going on. I wouldnt be surprised if you melted your head in the process... Not even a mix will be sufficient... You go 13.5:1 and youll need to run straight race gas (cam II or VP are best). If you decide to run pump fuel with that piston, be sure to post some pics for us when it blows up... You cant expect to run the highest compression possible in your engine and then try to save money by chintzing on the gas it needs. If you cant afford the gas, then dont do it and go with a mild 11:1 piston that will handle the pump gas...

[2muchquad]

i run 93 with 13.5 to 1 in my yz mx bike no problems,ran fine all of last season

[DirtDevilBT]

While I don't think its a good idea for a 400ex, there are some people with 450r running 13:1 pistons on good fresh 93. The amount of compression has a lot to do with you cam overlap and its bleed off. The 13:1 450r are running HRC cams. These have a lot of overlap due to their high rpm power range. Plus, these bikes are liquid cooled to keep everything stable.

My friend with his 440ex runs a wiseco 11.5 and Hot Cams S2 cam. He runs a 50/50 mix with no problems. And that's at Glamis hauling some serious asss all day long. If I were you, unless I missed something, I'd go with a big bore and 11.5:1 piston. His bike makes so much torque it's an eye popper, wheelies in any gear. Really a good package.

[kfxrider35]

how much is the vp goin for a gallon? im putting a 453 kit in my kfx and race web cams and some other stuff.