An overhead camshaft engine is a piston engine where the camshaft is located in the cylinder head above the combustion chamber.Single overhead camshaft SOHC engines have one camshaft per bank of cylinders. Dual Over Head Camshaft DOHC, also known as “twin-cam engines have two camshafts per bank.
If you are an automotive enthusiast, then you might have heard the terms SOHC and DOHC at some point. This presentation demonstrates the difference between both these engine head configurations and their working principles. Watch the video from Autotechlabs for more info:
A SOHC engine has one camshaft per bank of cylinders, therefore a straight engine has a total of one camshaft. A V or flat engine with a total of two camshafts one per bank of cylinders is a single overhead camshaft engine, not a double overhead camshaft engine.Regardless of number, the camshaft usually operates the valves indirectly via a rocker arm.
A double overhead camshaft (DOHC or “twin-cam”) engine has two camshafts per bank of the cylinder head,one for the intake valves and the other for the exhaust valves. Therefore there are two camshafts for a straight engine and a total of four camshafts for a V engine or a flat engine./wikipedia