11.1 Piston

[MAD400EX]

Will 400ex
11.1 piston run on pump gas

[400exdad]

Yes it will. However, it depends on a few factors. Thickness of base gasket and head gasket. If you don't change to a thinner one of either, you won't truly be getting 11:1... or anything close to it.

Check this out for great info:

http://www.exriders.com/vbb/showthread.php?s=&threadid=48435

I'll tell you what I did to mine if you want... I'll have to find it though... I write stuff down and forget it. :D

[400exdad]

Oh yeah, it also depends on the cam that you have. The amount of lift and especially overlap can really effect compression. Both can reduce the amount of compression stroke that a motor has. A more agressive or top end cam can reduce compression.