Conventionally, in an engine with a supercharger, an engine in which independent exhaust manifolds are respectively provided in a plurality of cylinder groups each including cylinders of the same phase among cylinders, so as to perform dynamic pressure supercharging is known.
In such an engine, an engine in which exhaust manifolds communicate with each other via an on/off valve in order to improve fuel consumption in a case where the engine is in a high speed region is publicly known. This engine is configured such that dynamic pressure supercharging exhaust manifolds can be changed to static pressure exhaust manifolds by bringing the on/off valve into an opened state. Accordingly, in the engine, by providing communication between the exhaust manifolds and increasing an actual pipe diameter, fuel consumption deterioration due to thermal losses can be suppressed. For example, this is as described in Patent Document 1.
In an engine described in Patent Document 1, in order to switch dynamic pressure supercharging exhaust manifolds to static pressure supercharging exhaust manifolds, a communication pipe providing communication between the exhaust manifolds and an on/off valve are required. However, in the engine to be operated by a dynamic pressure supercharging method for most of time using the engine, the communication pipe and the on/off valve enabling switching of the dynamic pressure supercharging method and a static pressure supercharging method are disadvantageously excessive facilities and a cause for increasing cost.