A composite engine block is disclosed including a main frame containing plural cylinder liner receiving cavities interleaved with plural cross walls extending generally perpendicularly between the outer side walls of the main frame and an oil pan adapter or ladder frame forming the lower section of the composite engine block between the main frame and the engine oil pan. Each main frame cross wall is combined with a pair of pillars extending between the upper head engaging surface of the main frame and a crankshaft bearing support located adjacent the lower surface of the engine block, wherein both the cross wall and pillars are shaped to strengthen and rigidify the composite engine block and to facilitate metal casting of the main frame. Size and weight reductions are realized by engine coolant flow paths within the main frame which bring coolant into contact with only the upper portion of each cylinder liner and lubrication flow paths in the main frame which cause the engine lubricant to return from the camshaft to the engine oil pan along a path which includes the space between the lower portions of the respective cylinder liners. Lubrication is supplied to corresponding main and camshaft bearings along single linear supply branches which intersect with a main lubrication rifle arranged parallel to and intermediate the rotational axes of the engine crankshaft and camshaft.