Cylinder head
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A 302/5.0L Ford cylinder head. |
In an
internal combustion engine, the
cylinder head sits atop the
cylinders and consists of a platform containing most part of the
combustion chamber and the location of the
valves and
spark plugs. In a
flathead engine, the mechanical parts of the valve train are all contained within the block, and the head is essentially a flat plate of metal bolted to the top of the
cylinder bank; this simplicity leads to ease of manufacture and repair, and accounts for the flathead engine's early success in production automobiles and continued success in small engines, such as lawnmowers. This design, however, requires the incoming air to
flow through a convoluted path, which limits the ability of the engine to perform at higher
rpm, leading to the adoption of the
overhead valve head design.
In the overhead valve head, the top half of the cylinder head contains the
camshaft in an
overhead cam engine, or another mechanism (such as
rocker arms and
pushrods) to transfer rotational mechanics from the
crankshaft to linear mechanics to operate the valves (pushrod engines perform this conversion at the camshaft lower in the engine and use a rod to push a rocker arm that acts on the valve). Internally the cylinder head has passages called
ports for the fuel/air mixture to travel to the inlet valves from the intake
manifold, for
exhaust gases to travel from the exhaust valves to the exhaust manifold, and for
antifreeze (coolant) to cool the head and engine.
The number of cylinder heads in an engine is a function of the
engine configuration. A
straight engine has only one cylinder head.A
V engine usually has two cylinder heads, one at each end of the V, although
Volkswagen, for instance, produces a
V6 called the
VR6, where the angle between the cylinder banks is so narrow that it utilizes a single head. A
boxer engine has two heads.
The cylinder head is key 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.
See also
*
Crossflow cylinder head*
Engine tuning*
Head gasket
