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The valve size difference becomes more obvious in the cylinder head asshown. The larger intake valve allows a good volume of air and fuel intothe chamber. The smaller exhaust valve tends to limit the outflow of hotgasses, which helps the engine make power. The engine makes the most ofthose hot, aggressive gasses because the exhaust valve acts as a trafficcop, keeping hot gasses and pressure contained in the cylinder forimproved cylinder pressure.