Can someone give me a volumetric efficiency formula to calculate the cubic feet per minute volume of and engine at a given RPM???

Ummmm

The actual volume of air at ambient temperature amd pressure vs the theoretical displacement.

Like 400 CI 4 stroke displaces 200 CI per turn of the engine in theory, but actually draws in 180 CI per turn is 90% VE

Regards
Pat
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The original poster needs to clarify the question.

"Nominal displacement" (converted to the units of your choice) x half (because of 4 stroke engine) x revolutions per minute x volumetric efficiency under the specific conditions involved = volume rate of flow.

The trouble is that the volumetric efficiency depends on a TON of variables and can often only be estimated. How accurate the estimate needs to be, and how much effort and calculation and simulation needs to be put into producing that estimate, depends on what you are doing with the outcome, and THAT is something you haven't told us.

for a 4 stroke engine:

displacement (cubic inches) x  RPM x vol eff%
---------------------------------------------   =  CFM
                3456

displacement (liters) x  RPM x vol eff%
---------------------------------------   =  CFM
                56.63369

2 stroke:
displacement (liters) x  RPM x vol eff%
---------------------------------------  =  CFM
                28.31685

ISZ

Thanks Guys