Typically, internal combustion engines have a trapped mass of air beneath the piston. During each revolution of the crankshaft, this trapped mass of air either compresses or expands, depending upon the stroke of the piston, thereby reducing the efficiency of the engine. To alleviate this problem, prior art arrangements vent the crankcase so as to allow the air to migrate in the crankcase between areas divided by, or demarcated by, the main bearing bulkheads. However, because the vent passages between the bulkheads are somewhat restricted, moving the air mass requires energy. This results in pumping losses which also have a negative effect on engine efficiency. In the present invention, by providing communication ports between cylinders having pistons that are 180.degree. out of phase, a less restricted passage is created, thereby reducing pumping losses.
Accordingly, an advantage of the present invention is to reduce pumping losses by providing communication ports between cylinders having pistons that are 180.degree. out of phase.
Another advantage of the invention is to provide better crankcase breathing which, in turn, allows more efficient oil return from the cylinder head to the oil pan and subsequently increased engine efficiency and fuel economy.