A fresh gas system for a piston engine has a collecting line for supplying fresh air to multiple individual lines. The fresh gas system has the collecting line which is unthrottled and a control unit for actuation of the additional valves is designed so that it subdivides a fresh gas charge of the combustion chamber which depends on the load state into two charging phases (A, B) within an intake time window (T). This is limited by the opening and closing of the intake valve such that it actuates the additional valve to close within the intake time window (T) at a closing point in (TS). This depends on the load state and then actuates it to open at a later opening point in time (TO) that depends on the load state of the piston engine.