700cc chamber is right. but the exit has to be right. It looks as the one I have is what tkg said. 700cc chamber but the exit ports are 3% smoller then the port on the engine.

I not sure, I hope some one know more about it. but, If your port on the engine is 100cc then your exit prot out of the chamber should be 3% less then that. If I can find the page the said all of then and what the testing was that they did to come up with this I will put it on here.

That is what I did on my 77cc engine. It seems to work good. Ugly but workeds good lol

Paul