Refinements of RFF and HLA Models Evaluated by Comparison with Measurement Results: Computer simulations to predict the dynamics of valve train components have contributed significantly to the reduction of development time for valve train components with improved performance and reduced friction. Further improvement of the mathematical model is still necessary for increased accuracy of prediction particularly of high-speed operation since increasing engine speed has been a part of engine development approaches to improve both performance and fuel economy. Valve train components must be designed to cope with high-speed operating conditions, e.g., more than 7,000 ~ 8,000 rpm. In the design process, it is important to determine the camshaft speed at which valve operation begins to jump off the cam profile. Engineers at Hatano Industries, CD Adapco, and Hatamura Engine Research developed a technique to measure dynamic valve lift and load on a finger follower with a roller on the valve train of a 1.5-liter, four-cylinder gasoline engine. The measurement results were used to refine the models developed for the finger follower with a roller and hydraulic lift adjuster (HLA). A test rig was constructed to measure key variables necessary to validate these individual models. The chapter consists of 8 pages including 13 figures.