Hi Paul and Jerry,

Here something on how to control the amount of air for the engine.  This
is from a SLR lens aperture.  The text below is from another web site.
The aperture could be control/made in any way you might find useful.

If this has been look at before.  Please disregard.

Marc Joseph



Here's a quick summary:

    Aperture indicates whether the opening in your lens is wide open
     or narrow
    You can control the width of the opening by changing the aperture
     setting from the camera
    A small aperture number (2.8) represents a WIDE opening in the lens
    A large aperture number (22) represents a NARROW opening in the lens

The aperture f-stop scale looks like this:

f/2.8, f/4.0, f/5.6, f/8, f/11, f/16, f/22

Now, this particular scale shows each aperture number changing by
something called a full stop of light(air).

When the aperture changes by a full stop, the amount of light(air)
landing on the camera's sensor is either doubled or halved.

Example:

    f/2.8 lets in /twice/ as much light as f/4.0
    f/4.0 lets in /half/ as much light as f/2.8

All main command dials don't just spin freely: they "click".

<http://en.wikipedia.org/wiki/File:Aperture_diagram.svg>

<http://en.wikipedia.org/wiki/File:Aperures.jpg>