![]() ![]() The other main advantage of OHC engines is that there is greater flexibility to optimise the size, location and shape of the intake and exhaust ports, since there are no pushrods that need to be avoided. A disadvantage of OHC engines is that during engine repairs which require the removal of the cylinder head the camshaft engine timing needs to be reset. A downside is that the system used to drive the camshaft (usually a timing chain in modern engines) is more complex in an OHC engine. This reduced inertia in OHC engines results in less valve float at higher engine speeds (RPM). The valves in both OHC and OHV engines are located above the combustion chamber however an OHV engine requires pushrods and rocker arms to transfer the motion from the camshaft up to the valves, whereas an OHC engine has the valves directly actuated by the camshaft.Ĭompared with OHV engines with the same number of valves, there are fewer reciprocating components and less valvetrain inertia in an OHC engine. ![]() This contrasts the earlier overhead valve engine (OHV) and flathead engine configurations, where the camshaft is located down in the engine block. In an OHC engine, the camshaft is located at the top of the engine, above the combustion chamber. Use of DOHC engines slowly increased from the 1940s, leading to many automobiles by the early 2000s using DOHC engines. The first production car to use a DOHC engine was built in 1910. Dual overhead camshaft (DOHC, also known as "twin-cam" ) engines have two camshafts per bank. Single overhead camshaft (SOHC) engines have one camshaft per bank of cylinders. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion chamber in the engine block. Valvetrain configuration OHC cylinder head (for a 1987 Honda D15A3 engine)Īn overhead camshaft ( OHC) engine is a piston engine in which the camshaft is located in the cylinder head above the combustion chamber. ![]()
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