One non-limiting object of the present invention is to provide modifications to conventional in line 6 cylinder engines capable of increasing their efficiency in operation. This includes modifying the central two adjacent piston and cylinder assemblies of the engines. The modifications involve (1) changing the camshaft so that the central two adjacent piston and cylinder assemblies have their four stroke cycles in phase rather than 180° out of phase, (2) providing a communicating passage between the combustion chambers of the central two piston and cylinder assemblies and (3) modifying either the hardware or programming for the control of the fuel injectors of the central two piston and cylinder assemblies so that they can be selectively controlled not to inject fuel during the operation cycle thereof. The modifications contemplates providing a new cam shaft in which not only the cams relating to the central two adjacent piston and cylinder assemblies are modified to change 180° out of phase to in phase, but the cams relating to other piston and cylinder assemblies in order to provide a somewhat balanced application of the driving forces during each cycle.