Why are more than two valves used?

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Some car and bike engines make use of more than one valves (3, 4 and sometimes 5) haven’t heard of 6 though! That’s apart from the minimal requirement of one inlet and one outlet valve. If additional valves are used, the area of intake of air fuel mixture, as well as exhaust area increases, thus leading to improved performance. Improved performance implies better volumetric efficiency, hence better combustion and ultimately an increased power supply. The valves in such engines are generally located within the combustion chamber for optimization of flame propagation. Apart from this, they have an added advantage of providing better cooling to the cylinder head due to increased surface area. Commonly used multi valve combinations are – 3 valves: One large exhaust valve and two smaller intake valves. 4 valves: Two exhaust valves and two similar or a bit bigger inlet valves. 4 valves: Two exhaust valves and three inlet valves, all of same size.