Multi valve EngineOne cylinder requires minimum of two valves, therefore 4 cylinder engines have minimum of 8 valves. One intake- and one exhaust valve in each cylinder.
16v engines have 16 valves. Therefore 4 cylinder 16 valve engine has 4 valves for each cylinder. Two intake- and two exhaust valves.
20v engines have 20 valves (daa...) Therefore 4 cylinder 20 valve engine has 5 valves for each cylinder. Two intake- and three exhaust valves.
16v and 20v engines are normally DOHC engines. DOHC means "Dual Over Head Cam". DOHC engine has two camshafts, one for intake- and one for exhaust valves.
The advantage of four or five vales in cylinder is that the sparkplug can be fitted in the center of the combustion chamber. When the sparkplug is in the center it provides short flame travel, resulting in rapid and relatively complete burning. Also due to the short flame travel, a compact combustion chamber with central sparkplug (or with dual ignition) reduces the engine's octane requirement.
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