A piston engine (10), in particular in a motor vehicle, has a plurality of cylinders (3) whose combustion chambers (4) are connected to a fresh gas system (5). The fresh gas system (5) has two gas paths, namely a full-load path (9) and a partial-load path (10), for at least one of the cylinders (3), through which the fresh gas (6) can be supplied to the respective combustion chamber (4). To this end, a valve arrangement (11) at the intake end is provided for controlling the fresh gas stream through the gas paths (9, 10) into the respective combustion chamber (4). For actuation of the valve arrangement (11), a control unit (13) is provided, the control unit being designed so that it permanently blocks the full-load path (9) through appropriate control of the valve arrangement (11) at partial load and actuates the partial-load path (10) for controlling the fresh gas stream and through appropriate control of the valve arrangement (11) at full load, it actuates at least the full-load path (9) for controlling the fresh gas stream.