In Turkish, "üstten çift eksantrikli (motor)". (DOHC) valvetrain layout (also known as 'dual overhead camshaft') is characterised by two camshafts located within the cylinder head,[1] one operating the intake valves and one operating the exhaust valves. This design reduces valvetrain inertia more than a SOHC engine, since the rocker arms are reduced in size or eliminated.

A DOHC design permits a wider angle between intake and exhaust valves than SOHC engines. This can allow for a less restricted airflow at higher engine speeds. DOHC with a multivalve design also allows for the optimum placement of the spark plug, which in turn, improves combustion efficiency.