[Tom Vaught]

I will post a little more about Volumetric Efficiency tonight in this post.

Volumetric Efficiency indicates how well an engine "Breathes".
Volumetric Efficiency is really a incorrect term for what is really happening.

Mass Flow is what really counts. But because people have used Volumetric Efficiency there is no real reason to Change to MASS EFFICIENCY.

In the BOOST Forum we can talk about MASS FLOW (because under BOOST conditions the MASS FLOW goes up while the Volumetric Flow remains the same as a Naturally Aspirated engine).

So V.E. (mass) is The Actual Mass of Air taken in (divided by) the Theoretical Mass of Air which could be taken in.

Highest Volumetric Efficiency reaches a high point close to where Maximum Torque occurs.
It does not follow exactly but many people assume that they are the same thing.

Stock Engines have a V.E of about 75%.
High Performance Engines have a V.E. of about 80% at max speed and 85% at max torque.
A Racing Engine can have a V.E. of 90%+ at max speed and a V.E of over 95% at max torque.

Again if we are talking DENSITY of the Air then V.E can be expressed as the Density in the Cylinder divided by the Density of the Ambient Air entering the engine.

IDEAL MASS FLOW FOR A 4-CYCLE ENGINE IS CALCULATED BY:

(ENGINE RPM DIVIDED BY 2) TIMES (CUBIC INCH DISPLACEMENT) TIMES (INLET AIR DENSITY).

Note: Air Density varies inversely with Pressure so:

The Lower the Pressure, the LESS DENSE the Air.

More Tomorrow.

Tom V.