Abstract: An engine block for a reciprocal piston internal combustion engine which is constructed from two substantially identical block halves. Each block half includes a mating surface formed around its outer periphery which is symetrical about the center line and a cylinder adapted to receive a reciprocal piston. Each block further includes a pair of manifold passageways wherein one end of each passageway is adapted to be connected to the cylinder through a valve means while the other of each passageway is open to the mating surface on opposite sides of and equidistantly spaced from the center line. A recessed channel is formed in the mating surface and extends from the other end of each passageway and to the outer edge of the mating surface. The engine block halves are secured together so that the mating surfaces abut together whereupon the recessed channels on one block half register with the recessed channels on the other block half.