Lightweight engine block cooling system

A lightweight engine block comprising:

• a thermally conductive casting forming a unitary cylinder housing and a bell-shaped, crankcase housing, the cylinder housing having at least one piston cylinder with a center axis and a cylindrical inner wall constructed to receive a reciprocating piston therein, the piston and cylinder defining a combustion chamber with a changeable volume when a piston reciprocates between a top dead center position and a bottom dead center position, the cylinder housing having an upper, liquid-cooled, cylinder section and a lower, air-cooled, cylinder section, wherein the upper cylinder section has a finless outer housing wall displaced from the cylinder wall, wherein a water jacket is formed between the inner cylinder wall and the outer housing wall around the combustion chamber above the bottom dead center position of a piston reciprocal in the cylinder, the water jacket having liquid cooling means for cooling the upper cylinder section, and, wherein the lower cylinder section has a plurality of outwardly directed cooling fins wherein the cooling fins extend between the outer housing wall of the upper cylinder section of the cylinder housing and the bell-shaped, crankcase housing wherein the fins are parallel to the center axis of the cylinder and both reinforce the engine block casting and cool the lower cylinder section.