VPT (Variable Piston Timing) utilizes a lightweight piston design that varies the piston displacements and the periods of the 4 strokes, produces a power stroke in every revolution, and more. VPT can incorporate electronic devices by on board computer to change the stroke ratios and the timing during engine operation.This article discusses VPT retrofit of a slow speed engine without electronics. Substantial horsepower, torque and some efficiency gains are achieved. The hardware changes are kept to a minimum. The first engine is scheduled to be tested in the third quarter of 1997. Electronic VPT will be included in the next generation engine.