Implementation
The number of cylinder heads in an engine is a function of the engine configuration. Almost all inline (straight) engines today use a single cylinder head that serves all the cylinders. A V (or Vee) engine has two cylinder heads, one for each cylinder bank of the 'V'. For a few compact 'narrow angle' V engines, such as the Volkswagen VR6, the angle between the cylinder banks is so narrow that it uses a single head spanning the two banks. A flat engine (basically a V engine, where the angle between the cylinder banks is now 180°) has two heads. Most radial engines have one head for each cylinder, although this is usually of the monobloc form wherein the head is made as an integral part of the cylinder.
Some engines, particularly medium- and large-capacity diesel engines built for industrial, marine, power generation, and heavy traction purposes (large trucks, locomotives, heavy equipment etc.) have individual cylinder heads for each cylinder. This reduces repair costs as a single failed head on a single cylinder can be changed instead of a larger, much more expensive unit fitting all the cylinders. Such a design also allows engine manufacturers to easily produce a 'family' of engines of different layouts and/or cylinder numbers without requiring new cylinder head designs.
The design of the cylinder head is key to the performance and efficiency 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.