2.2 options > is 10.5:1 too much?

[farleyd]

Hi, i ahve bought what appeared to be 10.5:1 85mm JE pistons.


Been told that they will be too much compression to run on pump gas. Ive read that there is 2 ways to reduce comp ratio:
1) use copper gasket between the cylinders and heads
2) remove material from the dome.

Any opinions?

[Tyson Schmidt]

Yes, that is too high for pump gas unless you twin-plug. You should install copper base gaskets that are .50mm thicker than what is required.

Example: Stock is .25mm, and if the heads were machined another.25, then you'd need .50mm base gaskets. Then, to lower the compression, you'd use a copper gasket that is another .50mm thicker, therefore, you'd install 1.0mm base gaskets. Depending on combustion chamber volume, this should roughly reduce the compression a half a point.

[Wayne 962]

You need to do the compression calc in order to make sure. Check Bruce's book for details...

-Wayne