Miller Cycle

[jac at wave.sheridan.wy.us]

The net effect of a Miller Cycle is to limit the maximum manifold pressure to a value that keeps the preignition cylinder pressure safe despite increased mechanical compression ratio.

This is similar to not pushing the gas pedal down all the way.

The reality is that a human cannot track the manifold pressure quickly enough in an automobile to prevent over pressure, particularly during low RPM acceleration.

In an aircraft the MAP can be reasonably limited by the pilot at low elevation because of the continuous load presented by a propeller. As the plane climbs, the throttle is opened to take advantage of the increased compression ration in the less dense air at elevation.

The economy benefits of the Miller Cycle are certainly attractive in an automobile, but a special cam is a big step that can be avoided.  Rather than  modifying the cam and valvetrain, a servo system can control the throttle advance so that the MAP is limited to safe value.  The whole system can be designed, built, debugged and tested prior to tearing the engine down to install the high compression pistons. The risk and cost of an incomplete project is quite low.

MAP would provide the feedback and knock detection would determine the maximum MAP.  This should be a quick and flexible home brew development.