CFM - Cubic Feet per Minute, could use cubic inch per minute just be ridicules sized numbers. Cid x RPM / 3456 = CFM.
No matter which way you slice it, Naturally aspirated, blown, turbo, large displacement, small displacement, high rpm, low rpm etc... is gonna have to displace a certain amount of fuel and air in certain amount of time to make a certain HP, within a given tolerance based on efficiencies. CFM is a "Displacement" of air "Cubic Feet" in time, a "Minute", RPM is based on same time "Revolutions Per Minute". Engines are measured in there static displacement "liters, cubic inch, even cubic feet if you wanted" a working engine ain't static. So a 250 cid at 10,000 rpm is "Displacing" the same amount of air as 500 cid at 5000 rpm given same VE%. so in that minute of time there the same size, same dynamic displacement.