JE 12:1 piston actual compression

[02MX400ex]

i may be buying a 400ex with a JE 12:1 piston in it. i need to know what the actual compression ration is for this piston. what kind of gas will i have to use.

[cals400ex]

the actually compression will vary depending on what gaskets you use and who cut the piston to that ratio. you will definately need to mix some race gas in there for sure.