An engine includes a first crankshaft and a second crankshaft, pistons, piston rods, cylinders, combustion chambers, and fuel injectors. The crankshafts each extend in a horizontal plane and form a first and second rotating power output shaft of the engine. The combustion chambers form containment boundaries for combustion reactions of an air-fuel mixture formed in the cylinders with fuel provided by the fuel injectors. The piston rods connect the pistons to the first or the second crankshaft. The pistons are disposed in the cylinders, and the planar surface of the piston head of each piston distributes forces from an associated combustion reaction to a corresponding piston rod. The piston heads are disposed at an angle between 7 and 15 degrees in the first bank of cylinders and 7 and 15 degrees in the second bank of cylinders relative to a vertical plane.

An engine includes a first crankshaft and a second crankshaft, pistons, piston rods, cylinders, combustion chambers, and fuel injectors. The crankshafts each extend in a horizontal plane and form a first and second rotating power output shaft of the engine. The combustion chambers form containment boundaries for combustion reactions of an air-fuel mixture formed in the cylinders with fuel provided by the fuel injectors. The piston rods connect the pistons to the first or the second crankshaft. The pistons are disposed in the cylinders, and the planar surface of the piston head of each piston distributes forces from an associated combustion reaction to a corresponding piston rod. The piston heads are disposed at an angle between 7 and 15 degrees in the first bank of cylinders and 7 and 15 degrees in the second bank of cylinders relative to a vertical plane.