Internal combustion engine cylinder head with port coolant passage independent of and substantially wider than combustion chamber coolant passage

An internal combustion engine cylinder head for being clamped to a cylinder block for defining therewith a plurality of combustion chambers arranged in a row, said cylinder block having a coolant jacket, said cylinder head being formed with:

• a plurality of intake ports each being opened in a first half side portion of each one of said combustion chambers for introducing intake air or mixture therein;
• a plurality of exhaust ports each being opened in a second half side portion opposite to said first half side portion of each one of said combustion chambers for exhausting combustion gases therefrom;
• a first coolant passage disposed along the row of said plurality of combustion chambers adjacent said plurality of intake ports so as successively to pass thereby as located on one side thereof remote from central roof portions of said combustion chambers;
• a second coolant passage disposed along the row of said plurality of combustion chambers adjacent said pluruality of exhaust ports so as successively to pass thereby as located on one side thereof remote from said central roof portions of said combustion chambers;
• and
• a third coolant passage disposed along the row of said plurality of combustion chambers adjacent said central roof portions of said combustion chambers so as successively to pass thereby;
• said first, second and third coolant passages each being independently connected at one end thereof with said coolant jacket of said cylinder block so as individually to receive coolant therefrom, thereby establislhing three parallel flows of coolant through said first, second and third coolant passages with a predetermined triple distribution of flow rates according to certain relative magnitudes of flow resistance of said three coolant passages.