A plot of dynamic camshaft forces from one of our valve train dynamics simulations. The forces are plotted against the angle of the camshaft, with zero being the high lift point. The green curves are the forces exerted by the spring for both an ideal massless spring and accounting for spring dynamic (spring surge) effects. The pink curves are the force exerted on the cam by the lifter for both an ideal stiff valve train and one with flexible pushrods and other components.