^^^^ that's right! (actually VE*CID*maxrpm/3456 where VE is volumetric efficiency)

Sometimes a quicker rule of thumb is CID*2 i.e. 383*2 -> 766cfm

this shortcut assumes max rpm~7000 (3456*2) and 100% volumetric efficiency (most motors are 80% to 95% efficient).... a 750cfm carb should suffice unless you're looking to spin the motor much over 7000rpm.

This is for minimum cfm required.... you can go larger but if you go too big the vaccuum signal will be too weak at lower rpm.

2 cents,

Chris