Cylinder head for a lean-burn gasoline engine

A lean-burn gasoline engine comprising:

• an air intake port having an air intake port inlet, an air intake port outlet, and an air channel connecting the air intake port inlet to the air intake port outlet;
• a combustion chamber 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 comprising a valve head bottom surface that faces the combustion chamber, a valve head top surface that faces the air intake port and a valve stem, the movable valve 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;
• a valve guide opening in a wall of the air channel opposite the top surface of the movable valve;
• and
• a valve guide passage extending into the wall and away from the valve guide opening, the valve guide passage housing a valve guide arranged to guide the valve stem and permit movement of the movable valve between the closed state and an opened state, the valve guide having a first end proximate the movable valve, the first end being positioned within the valve guide passage such that airflow through the air channel is not impeded by the valve guide;
• wherein the opening comprises a first edge distal from the air intake port outlet and a second edge proximal to the air intake port outlet;
• wherein the first edge of the opening defines a sharp transition, at a first angle, between the wall of the air channel within which the opening is provided, and a wall of the valve guide passage;
• and
• wherein the first edge has a radius of curvature of between zero and 3 mm.

A method of manufacturing a lean-burn gasoline engine, the engine comprising an air intake port having an air intake port inlet, an air intake port outlet, and an air channel connecting the air intake port inlet to the air intake port outlet, and a combustion chamber 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 comprising a valve head bottom surface that faces the combustion chamber, a valve head top surface that faces the air intake port and a valve stem, the movable valve 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, a valve guide opening in a wall of the air channel opposite the top surface of the movable valve, and a valve guide passage extending into the wall and away from the valve guide opening, the valve guide passage housing a valve guide arranged to guide the valve stem and permit movement of the movable valve between the closed state and an opened state, the valve guide having a first end proximate the movable valve, the first end being positioned within the valve guide passage such that airflow through the air channel is not impeded by the valve guide, the method comprising:

• providing a cast part;
• and
• cutting through the wall of the air channel, to form the valve guide opening and the valve guide passage;
• wherein a portion of the wall of the air channel at which the opening is to be formed is provided with a cast formation which extends into the air channel, the formation having a target surface substantially or generally perpendicular to an intended orientation of the valve guide passage starting at the target surface, wherein the cutting step comprises:
• a first cutting step, starting at the target surface, cutting away the formation, and forming the valve guide passage.