DOHC (Double Overhead Camshaft)

It allows four valves per cylinder and better breathing at high engine speeds. Separate camshafts make it easier to vary intake and exhaust timing independently. A V engine with DOHC heads has four camshafts in total.

A timing belt or chain drives both camshafts from the crankshaft, and the cam lobes open the valves directly or through followers.

More timing parts mean more components to inspect when the belt or chain is replaced. Timing marks on both camshafts must line up exactly during reassembly.