The ASA cars used to run a 9.5:1 CR rule---and still made tons of power. The engine builders just had to get better on the design of the combustion chamber. As Eric mentioned, flame travel across the top of the piston is probably one of the most important--and overlooked--areas of an engine build. In my days in an automotive machine shop, tall CR numbers were the only thing guys wanted to hear, on the alky engines, 15.0 to 16.5 was not that uncommon, but some of the combinations guys tried just didn't work, mainly because of, as Eric said, the dome configuration of the piston just wouldn't allow decent flame travel. Compressing the gas is great, but you've got to be able to fire it too!!!!! I've been out of the engine building part of it for better then 10 years now. Most of my knowledge on the CR and chamber stuff is terribly outdated.... I do know the people to get hold of when I have a question. The key, IMO to this and every aspect of building a Hot Rod is planning. Getting all the components to compliment each other instead of working against each other is critical....

We're really fortunate here at CHR to have such knowledgeable engine guys who offer the good information that works and not just throw out a bunch of theory that can't be substantiated.....