High compression type internal combustion engine

An internal combustion engine comprising:

• a cylinder block having a cylinder bore therein;
• a piston reciprocally movable in said cylinder bore and having a substantially horizontally extending flat top face;
• a cylinder head having an inner wall comprising a substantially horizontally extending flat portion and a recessed portion which is arranged at a periphery of said inner wall and has a circumferential wall and a bottom wall, said flat portion being arranged at a position close to the flat top face of said piston positioned at top dead center for forming a squish area therebetween, said piston and said cylinder head forming a combustion chamber therebetween;
• a helically shaped intake passage formed in said cylinder head and having an intake valve therein, said intake valve having a valve head which has a front face exposed to said combustion chamber, the front face of said valve head being arranged at a level which is approximately equal to a level of said flat portion;
• an exhaust valve arranged on the bottom wall of said recessed portion and having a valve head;
• said squish area comprising a first squish area portion and a second squish area portion which are divided by a straight line passing through an axis of said intake valve and an axis of said exhaust valve, said first squish area portion having an area which is about four times the area of said second squish area portion;
• a groove formed on said flat portion and extending from the valve head of said intake valve to said recessed portion, said groove having an approximately uniform depth which is slightly larger than the clearance between said flat portion and the flat top face of said piston positioned at top dead center, and;
• a spark plug having a spark gap arranged in said groove in the vicinity of said exhaust valve at a position near said second squish area portion and remote from said first squish area portion;
• a depression connected to said recessed portion formed on said groove, said depression having an inner wall which is connected to the circumferential wall of said recessed portion and on which the spark gap of said spark plug is arranged, the inner wall of said depression being arranged to be slightly inclined towards said recessed portion with respect to a vertical plane passing through the axis of said intake valve and the axis of said exhaust valve.