Effective stroke is what is left over after the Intake valve is at it's advertised closed position, which you have to input as Ica. This is a computer-generated number and not the real world number cuz; the number that you input as Ica is the fall-out from using advertised numbers in which the valve is not yet closed! At .008tappet rise, and with 1.5 rocker ratio, the valve could still be open up to;