Editing Overhead camshaft engine (section)

=== {{anchor|DOHC|Dual overhead camshaft|Twin cam}} Dual overhead camshaft (DOHC) ===
[[File:DOHC-Zylinderkopf-Schnitt.jpg|thumb|DOHC design (for a V12 engine)]]
A ''dual overhead cam'', ''double overhead cam'', or ''twin-cam'' engine has two camshafts over each bank of the cylinder head,<ref name=Hillier/><ref name=Stoakes/> one for the intake valves and another 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. 

A V engine or flat engine requires four camshafts to function as a DOHC engine, since having two camshafts in total would result in only a single camshaft per cylinder bank for these engine layouts. Some V engines with four camshafts have been marketed as "quad-cam" engines,<ref>{{cite web |title=Technically Interesting: Ford Indy DOHC V8 |url=https://bringatrailer.com/2018/04/26/technically-interesting-ford-indy-dohc-v8/ |website= Bring a Trailer |access-date=6 September 2022 |date=26 April 2018}}</ref> however technically "quad-cam" would require four camshafts per cylinder bank (i.e. eight camshafts in total), therefore these engines are merely ''dual overhead camshaft'' engines. 

Many DOHC engines have 4 valves per cylinder (sometimes 5, [[Audi]] or [[Volkswagen]] for instance).{{efn-la|However DOHC engines with two valves per cylinder include the [[Alfa Romeo Twin Cam engine]], the [[Jaguar XK6 engine]], the early [[Ford I4 DOHC engine]], 10V [[Volvo Modular engine]] and the [[Lotus-Ford Twin Cam|Lotus Ford Twin Cam engine]].}} The camshaft usually operates the valves directly via a bucket [[tappet]]. A DOHC design permits a wider angle between intake and exhaust valves than in SOHC engines, which improves the air-fuel mixture's flow through the engine. A further benefit is that the spark plug can be placed at the optimum location, which in turn improves [[combustion efficiency]]. Another newer benefit of DOHC engine design is the ability to independently change/phase the timing between each camshaft and the crankshaft. This affords better fuel economy by allowing a broader torque curve. Although each major manufacturer has their own trade name for their specific system of variable cam phasing systems, overall they are all classified as [[variable valve timing]].