the amount a venturi will flow is measured in cfm, so it relates directly to head porting and inlet manifolds, carbs etc. in that way.
The yanks measure their four barrel carbs in cfm rather than in actual size like the eyeties do Ie. a 600 Holley will flow 600 cubic feet per minute of air at wide open throttle, when attached to a big enough engine to do this!!!

Of course, it only relates to how much air can flow, not how it flows
Who says head porting is a black art