A control system is disclosed for operating an internal combustion engine. The control system includes a control unit configured for providing a part load mode that is optimized for slow operation of the engine at loads up to an upper part load limit in the range from 40% to 75% of a maximum engine load. The control unit is also configured for providing a high load mode for engine loads above the upper part load limit. In the part load mode, at least one inlet valve is closed at a closing angle later than in the high load mode.