PURPOSE: To greatly increase engine torque at the time of low revolution and high loading by selectively controlling an intake port and the intake valve of an over-head valve in a changeover engine between two-cycle and four-cycle, and concurrently controlling the supercharging air flow paths of turbo chargers provided in parallel.
CONSTITUTION: When an engine is operated in a form of two-cycle, intake valves 1a through 1d on the upper sections of cylinders are closed, intake ports in the skirt section are released to their maximum opening by a closing means, and the supercharging air flow paths of turbo chargers 3 and 4 which are arranged every two cylinders, are mutually connected in series with a valve 62 released. And high pressure supercharging air is fed with pressure via the intake ports by assisting the air compressing operations of compressors 32 and 42 with the rotating electric machines 33 and 43 electrically driven, which are provided for the turbo chargers, so that engine torque is thereby increased.