CFM rating is not really as important here as the size of the blade. Put a really big blade on a single carb motor and the air speed through the carb will be too low at lower rpms and make it a tuning nightmare. Especially on a nitrous motor with a tight converter............So, whats the answer, if we want to talk CFM, DON'T go to what is considered a 1250 throttle blade size.....too big