Internal combustion engine

In an internal combustion engine having:

• a combustion chamber formed between a top wall of a piston fitted in a cylinder and a lower wall of a cylinder head,
• an intake port formed through the cylinder head on one side of a reference plane in which a central axis of the cylinder is contained, said intake port communicating through an intake opening with the combustion chamber,
• an exhaust port formed through the cylinder head on an opposite side of said reference plane, said exhaust port communicating through an exhaust opening with the combustion chamber, and
• open/close valves disposed in the intake port and the exhaust port, respectively, the improvement comprising:
• the intake port is formed extending upstream from the intake opening substantially along the cylinder axis;
• and
• the piston is provided at the top wall thereof with a recessed portion and a raised portion, said recessed portion being formed at a location off-set toward said one side to guide an intake air flow, which has been inducted into the combustion chamber, as a swirl about an axis extending in parallel with a line which in turn extends at a right angle relative to the cylinder axis, and said raised portion being formed on the opposite side of said reference plane to extend in continuation with an upwardly gently sloping edge portion of the recessed portion, whereby the raised portion approaches the lower wall of the cylinder head at top dead center of the piston.