What does SOHC stand for?

SOHC stands for single overhead camshaft. It describes an engine with one camshaft positioned in the cylinder head above the combustion chamber, rather than in the engine block.

The camshaft opens and closes the intake and exhaust valves, either directly or through rocker arms. Because it sits above the valves, an overhead-cam design avoids the long pushrods used by overhead-valve engines. That generally reduces valvetrain inertia and helps an engine operate efficiently at higher revolutions.

“Single” can cause confusion. It means one camshaft per cylinder bank, not necessarily one camshaft for the entire engine. A straight-four SOHC engine has one camshaft, while a V6 or flat-six SOHC engine normally has one camshaft for each bank, making two overall.

SOHC is also distinct from DOHC, or dual overhead camshaft. DOHC engines use two camshafts per bank, commonly separating intake-valve and exhaust-valve operation. Early overhead-cam examples include the 1902 Maudslay and 1903 Marr Auto Car engines, long before the layout became common in modern vehicles.