A crossflow cylinder head is a

cylinder head In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinders and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas in more modern ...

that features the

intake An intake (also inlet) is an opening, structure or system through which a fluid is admitted to a space or machine as a consequence of a pressure differential between the outside and the inside. The pressure difference may be generated on the ins ...

and

exhaust Exhaust, exhaustive, or exhaustion may refer to: Law *Exhaustion of intellectual property rights, limits to intellectual property rights in patent and copyright law ** Exhaustion doctrine, in patent law ** Exhaustion doctrine under U.S. law, in ...

ports on opposite sides. The gases can be thought to flow across the head. This is in contrast to

reverse-flow cylinder head In engine technology, a reverse-flow or non-crossflow cylinder head is one that locates the intake and exhaust ports on the same side of the engine. The gases can be thought to enter the cylinder head and then change direction to exit the head. T ...

designs that have the ports on the same side. Crossflow heads use overhead valves, but these can be actuated either by

overhead camshaft An overhead camshaft (OHC) engine is a piston engine where the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion cha ...

s, or by a valve-train, which has the camshafts in the cylinder block, and actuates the valves with push rods and rockers. File:Culasse.gif , Crossflow cylinder head, with twin overhead cams File:Overhead camshaft with rockers (Autocar Handbook, 13th ed, 1935).jpg, Cutaway view of the overhead camshaft, rockers and valves of a crossflow cylinder head File:4-Stroke-Engine.gif, Cross-section of a four-stroke engine showing the flow of gases across the cylinder head from the inlet port on the right to the exhaust port on the left, via the combustion chamber

Advantages

A crossflow head gives better performance than a

Reverse-flow cylinder head In engine technology, a reverse-flow or non-crossflow cylinder head is one that locates the intake and exhaust ports on the same side of the engine. The gases can be thought to enter the cylinder head and then change direction to exit the head. T ...

(though not as good as a uniflow), but the popular explanation put forward for this — that the gases do not have to change direction and hence are moved into and out of the cylinder more efficiently — is a simplification since there is no continuous flow because of

valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...

opening and closing. But since there is overlap between the intake and exhaust profiles there is a point in which both valves are open. At that point the inertia of the exhaust gases leaving the cylinder helps to aspirate the intake gases into the cylinder. The other main reason for the better performance of crossflow is that the ports and valves can be larger and its physical separation of the hot exhaust manifold keeps the air in the intake manifold cooler. Most modern engines are of a crossflow design. The engineering terminology for these benefits is greater

volumetric efficiency Volumetric efficiency (VE) in internal combustion engine engineering is defined as the ratio of the mass density of the air-fuel mixture drawn into the cylinder at atmospheric pressure (during the intake stroke) to the mass density of the same volu ...

Examples

In the UK, "Crossflow" is also used to refer specifically to

Ford Motor Company Ford Motor Company (commonly known as Ford) is an American multinational automobile manufacturer headquartered in Dearborn, Michigan, United States. It was founded by Henry Ford and incorporated on June 16, 1903. The company sells automobi ...

's Kent Crossflow four-cylinder

overhead valve An overhead valve (OHV) engine, sometimes called a ''pushrod engine'', is a piston engine whose valves are located in the cylinder head above the combustion chamber. This contrasts with earlier flathead engines, where the valves were located b ...

engine, and its short-block "Valencia" derivative which has been used in cars from the 1960s up to the present day, albeit with the addition of fuel injection and a modern engine management system. The term was also briefly used in the early 1980s in Australia for the revised 4.1 litre inline six-cylinder engine in Ford's Australian large family car, the

Falcon Falcons () are birds of prey in the genus ''Falco'', which includes about 40 species. Falcons are widely distributed on all continents of the world except Antarctica, though closely related raptors did occur there in the Eocene. Adult falcons ...

. This was in response to the post-1979 fuel crisis where the Falcon was a comparatively fuel-inefficient car compared to its contemporary rivals.

Four valve heads

This term is used for engines which have two intake and two exhaust valves per cylinder; four (or five) valves per cylinder result in engines having superior high RPM performance sourced from total port circumference, rather than the relative location of the ports.

References

* {{Automotive engine , collapsed Cylinder head (crossflow)

Advantages

Examples

Four valve heads

See also

References