Herein disclosed is an automotive spark-ignition valve-in-head internal combustion engine of the type which has main and auxiliary combustion chambers wherein combustion is initiated in the auxiliary combustion chamber and the resultant flame squirts into the main combustion chamber through a flame passageway whereby the flame fronts radiates out throughout the main combustion chamber from the outlet end of the flame passageway. The outlet end of the flame passageway is located about a "small-clearance-volume" portion of the main combustion chamber so that the flame fronts travel from the small-clearance-volume portion toward a "major-clearance-volume" portion. The small-clearance-volume portion largely corresponds to a squish-quench area in a combustion chamber of the turbulence type such as the wedge combustion chamber.