Race Gas?

[TheBlasterMan]

Under what conditions do i have to run race gas ona 400 ex?

Porting? Polishing? High Compression?

Thanks TheBlasterMan

[6858-400ex]

higher comp piston

[44oEX]

you have to run it if you go any bigger then 11:1 on your compression, thats it.

[F-16Guy]

There is no magic number for compression ratios. It depends on a number of factors, including displacement, water or air cooled, other engine mods, piston design, combustion chamber design, etc. If you have a modified engine (because 99% of stockers will run on pump fuel), and it's jetted right and in good repair, the best advice would be to listen to it when you ride. If it pings and/or knocks pretty much all the time or under certain conditions (dunes, hot days, etc.), then you will know to run higher octane fuel when riding in those conditions. A 50/50 mix with super is usually plenty for all but very high compression ratio engines. I have an 11:1 Wiseco in my 400ex, and it runs fine on super everywhere but in the dunes; there I run at least 50/50.