1In the development of motorcycle engines, a strong feeling of power, an element of being fun to ride has continued strong demand. However, demand to meet environmental performance, a conflicting element, has increased dramatically in recent years and a breakthrough technology that achieves both environmental performance and a feeling of power is in demand.Here, the newly developed engine has greatly enhanced feeling of power while clearing stringent environmental restrictions through use of a centrifugal type supercharger.However, there were several problems that had to be resolved with regards to application of a supercharger to a motorcycle engine.In applying a supercharger to a motorcycle, a major problem is the best way to keep the engine size from increasing in size. The engine, which is the heaviest parts on a motorcycle greatly affects motorcycle maneuverability so it must be compact and the mass concentrated.Another one of the problems was suppression of knocking to the extent possible. An intercooler for cooling intake air is generally used as a countermeasure for knocking in supercharged engines. However, increase in size and weight of the motorcycle through use of an intercooler was cause for a significant loss in the fun to ride aspect and thus was difficult to permit. For this model, by increasing the supercharging efficiency of the supercharger and matching it to the engine characteristics suppression of intake air temperature and thus knocking was achieved. In addition, a layout that maximizes efficiency of the supercharger and that is beneficial to operability of the motorcycle was sought out.This report describes various technologies used to resolve problems that arise when applying a centrifugal supercharger to a motorcycle engine.