Patent ID: 7954471

Claim:
A spark ignited internal combustion engine, comprising: a combustion chamber having a side wall formed by a cylinder, a floor formed by a top surface of a piston, and a ceiling, and having a cylinder stroke volume of 0.3 liter or greater; a spark plug arranged on said ceiling and having its spark point located in said combustion chamber; and a cavity formed on said top surface of said piston, at least part of the cavity defining a spherical surface to which a hypothetical sphere having its center at said spark point contacts when said piston is at top dead center during a cylinder cycle, and said cavity being formed so that a ratio of V 2 to V 1 is equal to or greater than 0.31 and equal to or less than 0.37, where V 1 is a volume of said combustion chamber when said piston is at top dead center, and V 2 is a volume of part of said hypothetical sphere which does not interfere with any one of said floor and ceiling of said combustion chamber when said piston is at top dead center; wherein the engine has a geometric compression ratio of 13.0 or greater.