I have to admit I have never actually measured the compression ratio on any of my engines. All I do is cut out the squish band, if any, and then lower the cylinder to get a nominal piston to head clearance of .015 to .020".

Two things though... A small bore engine can tolerate a bit more compression before getting into detonation. Also, there are two ways to measure compression ratio with two strokes. One is full stroke, as is done with four stroke engines. The other is "effective compression ratio" which is measure from exhaust port closing; not full stroke. The two methods will give you very different numbers obviously. I am rather sure the numbers you quoted from O'Neils are full stroke compression ratios.

Also, E-85 will not work for our use, as it is made with ethanol, not methanol. Methanol is necessary for the catalytic reaction with the glow plug.

AV8TOR