Cylinder Head

The detachable top part of the of the cylinder block that houses the spark plugs, most of the combustion chambers, the intake and exhaust ports, and much or all of the valvetrain. It seals the cylinder and forms the top of the combustion chamber.

The cylinder head is fundamental to the performance of the internal combustion engine, as the shape of the combustion chamber, inlet passages and ports (and to a lesser extent the exhaust) determines a major portion of the volumetric efficiency and compression ratio of the engine.