Aluminum is the material for lighter structural components, and is also advantageous for the purpose of heat transfer. The automotive powerplant requires an efficient material with less weight and proper thermal characteristics, as demanded by early aviation applications, due to the recent necessity for environmental and energy conservation. However, cast iron has been the dominant material used for engine blocks because of simple economic reasons. To overcome the simple cost disadvantages of aluminum engine block application, it is necessary to utilize the full potential of the material to the proper advantage.New aluminum engine blocks with a unique cooling system of air assisted water cooling were developed. The basic design concept between cast iron and aluminum are the same, except for the design differences due to the structural stiffness of both materials. However, there are thermal property differences between aluminum and cast iron other than stiffness and weight. Therefore, the design method of the aluminum engine block was altered to take advantage of the thermal property.Practically, aviation and motorcycle engines use the air cooled aluminum block because of the lighter mass and high thermal conductivity of aluminum. This report describes a unique aluminum engine block for passenger vehicles. The cooling system is an air assisted water cooling method; the water jacket was shortened for upper core and thin fins replace lower part of core to dissipate the heat where the temperature is relatively low. This yields the reduction of radiator capacity and water pump size. It has also achieved significant reduction of block mass without loss of performance.