The timing of the intake valve opening event is generally governed by the opposing requirements of providing enough cam duration to allow the performance-justified maximum valve lift, and the need to minimize valve overlap to attain acceptable idle quality.
The optimal timing of intake opening was studied as an independent variable, by creating a family of cam lobes to be run through the WAVE one-dimensional engine simulation program. This allowed intake opening to be varied without changing the other three valve events or valve lift, for a variety of intake closing timings. The engine simulation results were then experimentally verified with engine dynamometer tests.
The results indicate that the optimal intake valve opening time for maximizing the area under the power curve, is much later than traditionally thought, and this can lead to high specific torque and power engines with exceptional idle quality. Some combustion rate benefits were found for delayed intake opening.