Any car buffs here? Just trying to make sure that I understand (because I am currently confused) about how to convert calculations of air between mass and volume. The problem I am trying to solve is calculating the Volumetric Efficiency of an engine at specific points in time. I have a scan tool that will report the following items: Flow of Air into the engine in grams/second Intake Manifold Absolute Pressure (in Hg or KPA) Intake Air Temperature (F or C) etc. I know the "volume" of my motor, but how do I convert gm/sec into a given volume. Is this just a matter of me understanding the ideal gas law? PV=nRT I am just not for sure that I am getting all the measurements converted to the appropriate values. For example, assume I have an engine that is 5.7L in size (or ~346 cubic inches). At 100% volumetric efficiency, the motor should consume and expel 5.7 liters of air (although fuel is also pumped into the combustion chamber) every 2 revolutions of the crankshaft. Can anyone shed any light on this for me? Theories abound on the car forums, but I am not for sure they really know. One popular formula is: VE = (3456 x CFM) / (CID x RPM) CFM = Cubic Feet per Minute of Air CID = Cubic Inch Displacement RPM = duh Not for sure how this calcuation was developed. The device on most modern cars reports air coming into the motor in terms of g/s. So, if there is an easy conversion of air from g/s to CFM, I can do that (I think). If I posted this in the wrong forum, my apologies.