1. ABSTRACTRecently, customer requirements for engines have become more demanding, not only in terms of power, but also for fuel economy. To deal with these demands, the four-valve per-cylinder engine is now widely used for passenger cars. The direct acting systems and roller rocker arm system are two major valve train systems for passenger car engines. The advantage of a direct-acting system is its simple mechanism and low cost. However, it has higher friction than a roller rocker arm system.To improve on this situation, we at FujiOozx have worked on reducing the moving mass for the direct acting system. Using newly-developed lightweight valve train components, moving mass was reduced by 28%. Consequently, approximately 40% of friction loss was eliminated and improvement of noise and smaller engine package size were achieved (with optimization of cam profile and valve spring) to create a lightweight, direct-acting valve system.