A snowmobile includes an engine including an engine head including a cylinder head, a supercharger, an intake manifold, throttle bodies, first joints that connect the intake manifold to the throttle bodies, second joints that connect the throttle bodies to the cylinder head, and a restrictor that connects the engine head to the first joints. The restrictor includes an engaging member that fits into grooves of the first joints, and connectors that connect the engaging member and the engine head to each other. A steering shaft is inserted between two mutually adjacent first joints which have a distance from each other greater than a distance between the other two mutually adjacent first joints.

Various methods and systems are provided for an intake manifold for an engine. In one example, an insert comprises an annular body having a top surface, bottom surface, inner surface, and outer surface. The insert further comprises a first groove for coupling an intake air port of an intake manifold to a cylinder head, a second groove for circulating gaseous fuel received from a gas runner of the intake manifold, and one or more openings to fluidically couple the second groove to an interior of the intake air port. The insert is configured to mix gaseous fuel and intake air at a coupling location between the intake manifold and the cylinder head.

A motorcycle including a protection cover for a throttle body that is less likely to contribute to an increase in the vehicle weight to thus improve the attachability thereof. A motorcycle includes a throttle body provided with a throttle valve for controlling a flow rate of intake air into an internal combustion engine and an air cleaner for supplying air to the throttle body. The throttle body is arranged at a rear of the air cleaner with an intake port of the internal combustion engine being arranged at a rear of the throttle body. The air cleaner includes a throttle body protecting section for covering at least a lower surface of the throttle body.

A separation chamber type anti-surge valve may include a valve body formed with a charge air passage inlet and a charge air passage outlet, and a valve cover coupled to the valve body by a fastening member to define an empty inner space between the valve body and the valve cover, in which the inner space is divided into a diaphragm chamber and a bypass chamber by a valve guide, one side tip of a valve rod being fixed in the diaphragm chamber, a valve disc fixed to another side tip of the valve rod, and the diaphragm chamber is divided into a control pressure chamber and a normal static pressure chamber.

A separation chamber type anti-surge valve may include a valve body formed with a charge air passage inlet and a charge air passage outlet, and a valve cover coupled to the valve body by a fastening member to define an empty inner space between the valve body and the valve cover, in which the inner space is divided into a diaphragm chamber and a bypass chamber by a valve guide, one side tip of a valve rod being fixed in the diaphragm chamber, a valve disc fixed to another side tip of the valve rod, and the diaphragm chamber is divided into a control pressure chamber and a normal static pressure chamber.

An intake sound amplifier amplifies intake sound that is transmitted from an engine mounted in an engine compartment of a vehicle to a cabin. The intake sound amplifier includes a first passage branched from an intake passage, through which intake air is introduced into an engine; a device body that includes a vibrating body vibrated by pulsation of the intake air and is connected to a downstream end of the first passage; and a second passage that is connected to a downstream end of the device body and extends to the cabin side. The device body is located outward in a vehicle width direction of a side frame that extends in a vehicle front-rear direction and separates inside of the engine compartment from outside in the vehicle width direction.

A watercraft propulsion system includes a propulsion unit to be driven by an engine. The engine includes a cylinder block, an air intake channel, an exhaust channel, a supercharging device, and a fuel injector. The watercraft propulsion system includes the engine, the propulsion unit to be driven by the engine, a rotation speed sensor to detect a rotation speed of the engine, an air intake pressure sensor to detect an air intake pressure of the engine, and a controller. The controller is configured or programmed to compute a command fuel injection amount so that the engine performs a combustion operation at an air/fuel ratio in a lean-burn range (lean-combustion range) according to the rotation speed detected by the rotation speed sensor and the air intake pressure detected by the air intake pressure sensor, and to drive the fuel injector based on the computed command fuel injection amount.

An outboard motor includes an engine, a pressure charger, an intercooler, a bypass air passage, and an air bypass valve to open and close the bypass air passage. The engine includes a cylinder block and an air intake passage and an exhaust passage both of which are connected to the cylinder block. The pressure charger is located in the air intake passage. The intercooler is located in the air intake passage between the cylinder block and the pressure charger. A first end of the bypass air passage is connected to a region of the air intake passage upstream of the pressure charger. A second end of the bypass air passage is connected to a region of the air intake passage downstream of the pressure charger. The air bypass valve is directly attached to the intercooler.

An air intake duct 8 is fixed to a rear of a cab 3 of a transport vehicle to extend vertically, air intakes 6a, 6b, 6c, 6d, 6e and 6f being opened on an upper portion of the air intake duct for suction of fresh air through the intakes as engine intake air. The air intake duct 8 is constituted by a blow-molded duct body 9 and an internal partition component 10 enclosed in the duct body in blow molding of the duct body 9 to partition an interior of the duct body 9 into a plurality of channels A, B, C, D, E and F reaching the air intakes.

Air induction systems are for an internal combustion engine. The air induction systems comprise an air intake plenum that conducts intake airflow to an air cleaner for cleaning prior to combustion in the internal combustion engine. The air intake plenum is movable with respect to the air cleaner between an open position separated from the air cleaner and a closed position connected to the air cleaner. A bellows connects the air intake plenum to the air cleaner when the air intake plenum is in the closed position. The bellows has an upstream first end that seals with the air intake plenum and a downstream second end that seals with the air cleaner.