For more than a decade there is a progressive demand for fuel efficient and high specific power output engines. Optimization of engine cooling and thermal management is one of the important activities in engine design and development. In the present paper an effort has been made to simulate the heat transfer modes of cylinder block and head for a present 4-stroke air-cooled motorcycle engine. Two and three-dimensional decoupled and conjugate heat transfer analysis has been done with commercially available computational fluid dynamics (CFD) codes. Experimental results are also presented. A complete simulation model has been developed and CFD techniques have been applied to design and optimize air cooling surfaces of cylinder head and block, for an air cooled motorcycle engine. The two dimensional analysis is an easy and fast method to predict fin surface temperature, heat transfer co-efficient and flow velocity. Three dimensional analysis gives detail information for heat transfer but it is computationally expensive. A good correlation has been observed between computational and experimental results. From the thermal point of view, a method has been developed for design and optimizing air cooling of cylinder head and block for air cooled motorcycle engine. Copyright © 2006 SAE International and Copyright © 2006 SAE Japan.