[H. L. Chauvin]

Hi Lopez,

This may or may not help one to visualize why one's performance engine, (even after 25,000 miles from now), will never idle at such low rpms as that of one's original stock Model A engine.

1. The pistons in both Model A engines will travel the same distances up and down.

2. The stock head has a larger combustion chamber that contains a larger volume of air than that of the high compression head which has a smaller combustion chamber; hence, one's performance engine contains a smaller volume of air before the piston begins to move downwards.

3. As the pistons in both engines travel the same distance downwards, the stock engine's combustion chamber has more air to begin with than the that of the high compression engine.

4. Because a vacuum can be translated into a container which has less air, the stock engine with more air will have less vacuum ........ and the high compression engine will have more vacuum because it had less air when it began descending.

5. More vacuum in a combustion chamber means more fuel drawn into the combustion chamber; and more fuel means more rpms ...... like opening the throttle.

6. Not trying to make one cough up their hot coffee; but if one drills small holes in one's intake manifold, and decreases the vacuum in one's performance engine's combustion chamber, by trial and error, one may be able make this performance engine idle at lower rpms to match that of the slow idling of one's stock engine.

7. Or for a final experience, one can drive to a race track where guys have very high performance engines, with terrific vacuums, with engineered matching racing cams.

8. Next, just crank up one's Model A and ask the race track driver if his car can idle this slowly to where he can see the individual fan blades rotating.

Hope this helps a little.