The theoretical CFM for any specific RPM is easy to calculate. Multiply 1/2 the cubic inch displacement times the RPM, which gives "Cubic Inches Per Minute", then divide that figure by 1728, the number of cubic inches in a cubic foot.
For instance: 350 cubic inches divided by 2 = 162.5
162.5 X 4000 = 650,000
650,000 / 1728 = 376.1 CFM at 4K RPM
To get real-world volume instead of theory, use 90% of the theoretical CFM as a ballpark figure. This accounts for various flow characteristics that prevent all the mixture and exhaust gas from flowing completely through the engine.
376 X .9 = 338.5 CFM
Most people don't understand that the maximum CFM of a carburetor is seldom, if ever used. It makes a good talking point to brag about a carburetor's maximum capacity, but in real world terms, that figure is virtually meaningless!
Jerry
