The design and testing of a centrifugal controlled variable camshaft phasing device for small-block Chevrolet engines

One method of improving performance and efficiency of internal combustion engines is to vary the timing of the valve opening and closure while leaving the lift and duration constant. This is called variable camshaft phasing and, generally, the camshaft should be advanced at low engine RPM and retarded as engine speed increases. The purpose of this project was to design and test a mechanically variable camshaft phasing device that retards the camshaft continuously over a given engine speed range as a function of engine speed.

It was desired to design a device that would fit on an unmodified engine block utilizing an unmodified camshaft that could fit under a slightly modified timing cover. A conceptual design was developed based on analysis of various geometries. Computer simulations were employed to search for the optimal kinematic configuration that would give the device a minimal torque dependency. Several different types of springs were then analyzed using both computer models and static testing that would allow the device to operate over the desired range of engine speeds.

A prototype variable cam phasing device was built and tested in a 1970's model Chevrolet small-block V8 driven by the Mechanical Engineering Department's engine dynamometer. The device exhibited unacceptable wear and fatigue characteristics in some areas of the device. However, the data that was gathered is encouraging and indicates that the prototype device represents a viable design.