A CYLINDER HEAD FOR A LEAN-BURN GASOLINE ENGINE

A lean-burn gasoline engine (110) is described, which comprises an air intake port having an air intake port inlet, an air intake port outlet, and an air channel (45) connecting the air intake port inlet to the air intake port outlet, a combustion chamber (50) having a combustion chamber inlet being connected to the air intake port outlet, the combustion chamber inlet having a throat where the air intake port outlet meets the combustion chamber inlet, a movable valve (51) comprising a valve head bottom surface (61) that faces the combustion chamber (50), a valve head top surface (62) that faces the air intake port and a valve stem (53), the movable valve (51) being arranged to move between a closed state for closing off the combustion chamber inlet and an opened state wherein intake air can flow from the air intake port into the combustion chamber (50), and a valve guide opening (69) in an upper wall of the air channel opposite the top surface (62) of the movable valve (51), and a valve guide passage (66) extending into the upper wall and away from the valve guide opening (69), the valve guide passage (66) having a passage wall and housing a valve guide (65) arranged to guide the valve stem (63) and permit movement of the movable valve (51) between the closed state and an opened state. The valve guide opening (66) comprises a first edge distal from the air intake port outlet and a second edge proximal to the air intake port outlet, the first edge defining a sharp transition, at a first angle, between the upper wall and the passage wall of the valve guide passage (66).