Cylinder head structure of an internal combustion engine

An internal combustion engine with a plurality of cylinders arranged in a row and having two intake valves and two exhaust valves for each cylinder, each cylinder having a combustion chamber formed therein by a cylinder head and a piston, said engine comprising:

• a pair of intake ports for each cylinder arranged adjacent to each other and on one side of a center line of said row of said cylinders, said intake ports arranged side by side and in a direction parallel to said row of said cylinders;
• a pair of exhaust ports for each cylinder arranged adjacent to each other on another side of said center line, said exhaust ports arranged side by side in said direction and being separated so that their centers are at a distance apart which is larger than a distance at which centers of said intake ports are separated;
• and
• squish means, provided between said exhaust ports in each cylinder, for reducing a cylinder volume between said cylinder head and said piston and causing a squish flow of air-fuel mixture on a side of said combustion chamber near said exhaust ports.