The heat transfer process has always played an important role in internal combustion engine design. An area of importance is the thermal loading of engine structural components, and the optimisation of engine cooling system. The engine cooling system of a vehicle makes up a significant portion of the total component cost.It also places demands on other vehicle systems, and the quality of its design is evident to the customer in terms of the power that it consumes that for a two-stroke engine with forced convection air cooling can be also the 10% of the total brake power. An area of importance is the calculation of the thermal load of engine structural components, and the optimisation of engine cooling system. Optimisation of engine cooling requires the solution of the coupled problem of heat transfer from gases to walls and of heat convection from the structure (generally a finned surface) to the external environment.The aim of this work is to furnish some reference data about the heat transfer process and to fix some criteria to optimise the air cooling system, paying attention to the field of small displacement (50-250 cm3) two-stroke engines.