Intake system of an internal combustion engine

Claim 1

An internal combustion engine having a cylinder head, at least two cylinders, each having a combustion chamber and an intake valve, at least two intake port passages formed in the cylinder head and connected to the corresponding combustion chambers via the corresponding intake valves, each of said intake port passages comprising a port terminating portion having a circumferential wall formed around a valve stem of the corresponding intake valve and an inlet port portion having an opening which is open to said port terminating portion, and a common connecting passage formed in the cylinder head and interconnecting said port terminating portions to each other, said common connecting passage having openings formed at opposite ends thereof, each opening being open to said corresponding port terminating portion at a position opposite to the opening of said corresponding inlet port portion with respect to the valve stem of the corresponding intake valve, wherein the improvement comprises: the opening of said inlet port portion and the opening of said common connecting passage which are open to the same port terminating portion are oppositely tangentially connected to the circumferential wall of said same port terminating portion towards a same circumferential direction; each of said inlet port portions has a minimum cross-sectional portion; and said common connecting passage has a uniform rectangular cross-section over the entire length thereof, the cross-sectional area of which is 0.5 to 1.0 times the cross-sectional area of said minimum cross-sectional portion of the inlet port portion.