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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.

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.

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