Aero Nut,

I'm still in RC glow mode, I guess. [:@] Yes, the Oneill heads take a sparkplug for spark ignition. This thread is not about that at all. Sorry guys. New here.
What threw me was the referrence to alcohol in the last two heads. But that would still be on ignition, of course.

In any case, it looks like gas or alcohol, both respond to about the same CR.

I think Ralph is just looking for a trial and error starting point to get his feet wet in raising the compression ratio.

And I guess I was kind of wondering too what benefit we might see with a gas to glow conversion if the CR and the port timing could be fiddled with in combination.

That sort of thing sounds like a whole new thread.

But for the moment, if you shave some off the bottom of the cylinder, or the top of the case, you'll bring down the cylinder some and increase the comrpession ratio. That would mean your timing would be affected, maybe to the better, maybe not. If not, does that mean you have to grind into the ports, bypass AND exhaust to bring the timing back to specs? What of disturbing the integrity of the plating. Will it peel?

Here's a thought. Say you drop the cylinder down too much, not enough to bump the piston, but clearly overcompressed. In that case, could you not just shave some material off the top of the piston to decrease the CR? Yes, you'd be very careful not to let any shavings go astray but it could be done, I think.