Intake system construction for internal combustion engine and manufacturing process of intake passage section of internal combustion engine

摘要

An intake system construction according to the present invention for an internal combustion engine is provided with a combustion chamber formed with upper and lower extremities thereof defined by a cylinder head and a piston, an intake open end arranged for being opened or closed by an intake valve, an exhaust open end arranged for being opened or closed by an exhaust valve, an intake port formed extending upwardly from the intake open end so that a vertical swirl of inducted air is formed in the combustion chamber, and an exhaust port for discharging combustion gas from the combustion chamber. The intake port is formed wider in one of halves thereof located adjacent a reference plane, which contains a central axis of a cylinder, than in the other half thereof located remote from the reference plane. The intake port is provided at a lower extremity thereof in the one half thereof with a raised portion for guiding an inducted air flow in the intake port toward an inner peripheral surface of a side wall of the cylinder.