The material and structure of the valve are also carefully designed. The intake valve is generally made of medium carbon alloy steel, such as chrome steel, chrome-molybdenum steel and nickel-chrome steel, while the exhaust valve is made of heat-resistant alloy steel, such as silicon-chrome steel, silicon-chrome-molybdenum steel, silicon-chrome-manganese steel, etc. The valve consists of a head and a stem. The head is used for sealing and usually adopts a 45° cone design. In order to increase the intake volume, the intake valve is usually designed to be larger than the exhaust valve.