Ralph,

Those are good questions. I'm inclined to think that if one could play with compression ratio and port timing independently, one might be surprised at the gains with a gas/glow mix. With my modified Tanaka, I can do that easily by shaving the base of the CASE by two or three gaskets and then add or delete them to tweak port timing and then compensate for and or tweak the compression ratio with shims under the bolt on head.

I had to butcher the Tanaka to do this, not something most can do but the O'Neill engines are done, right out of the box.

So far, at 7K on an 18 X 6 Zinger, the Tanaka, in its stock form is under the Zenoah. I hope to get it to at least 8K but it sure does sound sweet as it is. What a roar. These old ears have been enduring 19 to 22K for too long, I think. [:@]