What does 'DOHC' stand for?

DOHC stands for double overhead camshaft.

A DOHC engine places two camshafts above each cylinder bank in the cylinder head. Usually, one camshaft operates the intake valves and the other operates the exhaust valves. Because the camshafts sit near the valves, the design avoids the long pushrods required by an overhead-valve engine.

The arrangement can improve valve control at high engine speeds and gives designers more freedom to position intake and exhaust valves. Many DOHC engines use four valves per cylinder—two intake and two exhaust—which can improve airflow and breathing. Variable valve-timing systems can also adjust the camshafts’ relationship to the crankshaft to broaden the useful torque range and improve efficiency.

“Dual overhead camshaft,” “double overhead cam,” and “twin-cam” are commonly used names for the same basic configuration. The number of camshafts depends on engine layout: a straight-four DOHC engine normally has two camshafts total, while a V engine has two per cylinder bank, or four overall. DOHC should not be confused with SOHC, which uses one overhead camshaft per bank, or OHV, whose camshaft sits in the engine block.