Overhead cam

Overhead camshaft (OHC) valvetrain configurations place the camshaft within the cylinder heads, above the combustion chambers, and drive the valves or lifters directly instead of using pushrods.

Overhead cam

When compared directly with pushrod (or I-Head) systems with the same number of valves, the reciprocating components of the OHC system are fewer and in total will have less mass, although the engine as a whole will tend to take up a larger space and is more costly to manufacture and maintain. Though the system that drives the cams may become more complex, many engine manufacturers accept the added complexity in trade for better engine performance at very high RPM's, atypical of normal use. The OHC system can be driven using the same methods as an I-Head system, these methods may include using a timing belt, chain, or in less common cases, gears.

Many OHC engines today employ Variable Valve Timing and multiple valves to improve efficiency and power. OHC also inherently allows for greater engine speeds over comparable cam-in-block designs.

There are two overhead camshaft layouts:

Single Overhead Cam

See Main Article Single Overhead Cam

This arrangement denotes an engine with one cam per head. So if it is an inline 4-cylinder or inline 6-cylinder engine, it will have one cam; if it is a V-6 or V-8, it will have two cams (one for each head).

Double Overhead Cam

See Main Article Double Overhead Cam

A double overhead cam engine has two cams per head. So inline engines have two cams, and V engines have four. Usually, double overhead cams are used on engines with four or more valves per cylinder - a single camshaft simply cannot fit enough cam lobes to actuate all of those valves.

Camshaft - Cam overhead - Single overhead cam - Double Overhead Cam - Cam piston - Cam lobe - Cam valve

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