air flow rate may be determined via subtracting a filtered value of engine or cylinder air flow rate from the engine or cylinder air flow rate in other example other approaches such as taking a derivative of cylinder air flow rate may also be used to determine the rate of change of engine or cylinder air flow rate method 600 proceeds to 618 after the rate of change of engine or cylinder air flow rate is determined at 618 method 600 looks up empirically determined gain adjustments for intake and exhaust valve overlap duration intake and exhaust valve overlap position relative to crankshaft position engine speed and engine load the gain adjustments may be empirically determined and stored in table and or functions that are indexed via intake and exhaust valve overlap duration intake and exhaust overlap position relative to crankshaft position engine speed and engine load method 600 proceeds to 620 after gain adjustments are determined at 618 at 620 method 600 multiplies the base gain blow through amount rate of change of engine or cylinder air flow rate and gain adjustments from 618 to determine the volumetric efficiency correction that is to be added to the cylinder air amount during conditions where blow through is zero the base gain from 614 is multiplied by the rate of change of engine or cylinder air flow rate and the gain adjustments from 618 when blow through is present the blow through amount is multiplied by the rate of change of.