[400exRidah]

Hey guys I know my 400ex will be needing a rebuild pretty soon and I was wondering if I should get a high-compression piston or just stay with my 10:1? Are there benefits or drawbacks of getting a high-compression piston? Fill me in because I need some info. Thanks guys

 

[Here 2 help]

A high compression piston will give a boost in low end power and will require higher octane fuel. The higher compression and slower burning higher octane fuel may lower the RPM at which power peaks and increase the heat that the engine needs to dissipate. This may be a benefit for track racing, but might be a disadvantage for a woods rider. Unless you intend to ride at primarily high speed and are OK with buying 100 to 103 octane fuel, I would recommend just staying with the stock compression and using 93 octane pump fuel.

 

[400exRidah]

Oh thanks so much for the info. Sounds like I should stay with the stock compression bcz I am planning on doing a fair deal of trail riding and don't really want to have to buy really expensive fuel just for that. One more question. Does higher octane fuel do anything other than stop "four-stroking"?

 

[Here 2 help]

High octane fuel will not stop "four-stroking". Four stroking is a reference to a two stroke engine that is firing on every other stroke usually caused by the engine being flooded or running too rich due to a carb problem.

Japanese manufacturers usually specify about a 93 octane fuel for their modern engines. Most states in the U.S. blend alcohol with fuel to extend the fuel supply. Alcohol has a higher octane than gas so blending alcohol with 89 octane gas will result in an octane rating of about 93, but...... Japan does not mix alcohol with their gas. In Japan, 93 octane is 93 octane. If you use regular 87 octane pump gas, you are actually getting about 82 octane gas mixed with alcohol.