Abstract: A variable displacement engine is provided with a group of variably operated cylinders which are controllable to start and stop operation under predetermined operating conditions, and a group of invariable operated cylinders which are constantly in operation irrespective of the operating condition. The engine is operably connected to a variable displacement control system operable to deactivate the operation of the group of variably operated cylinders under predetermined operating conditions, such as idling, highway cruising speeds, and the like, so that the overall fuel efficiency of the engine is improved. In an aspect of the present invention, a turbocharger is provided. The turbocharger includes an inlet for receiving exhaust gas from the invariable operated cylinders and an outlet for supplying compressed air to the variable operated cylinders. In one embodiment, the engine is a reciprocating piston type engine, and in another embodiment, the engine is a rotary piston type engine.