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Recently, utilization of CFD (Computational Fluid Dynamics) at the initial stage of motorcycle development is increasing the importance and is becoming indispensable to environment matters. This paper describes a CFD system, which was developed based on PCC (Partial Cells in Cartesian coordinate) method CFD code. The code does not require the mesh generation at each computation. The merit of this system is a full automation after the solid modeling by a 3D-CAD system, such as geometry data transferring, starting of processes, and mailing the results. Moreover, an example of a combination between CFD and DOE (the design of experiment) will be explained. It is an application of an exhaust muffler design of motorcycles. In the past, the decision concerning to the power output during an exhaust muffler design could be done by only a few skilled engineers, but the decision became possible to designers who use this system.

New valve control system (HYPER VTEC:Variable Valve Timing and Lift Electronic Control System) having valve inactive mechanism which engine power is made to be united to the environment conservation was developed for motorcycle engines of sport type having higher engine speed. Mass increase in the valve operating system of this system is kept to a minimum with a compact, simple mechanism. The system enables high engine speed up to 13,500 rpm without abnormal motion of valves, having high reliability and durability. In addition, the valve control system has the enhancement of fuel economy and the effect of decreasing the intake and exhaust system sound during 2-valve operation. The switching mechanism part of the operating valve number was manufactured by cold forging, and has decreased costs. This system has been adopted to the sport type motorcycle CB400SF for domestic model in 1999.