The camshaft mounting position of the engine has three forms: lower, center, and top. Due to the high speed of the car engine, the rpm can reach more than 5,000 rpm. In order to ensure the intake and exhaust efficiency, the intake valve and the exhaust valve are used in the inverted form, namely the overhead valve device, which is suitable for the camshaft. The three installation forms. However, if a lower-mounted or mid-mounted camshaft is used, because the distance between the valve and the camshaft is relatively long, auxiliary components such as a valve lifter and a tappet are required, resulting in a large number of valve transmission mechanisms, a complicated structure, and a large engine volume. It is also easy to produce noise at high speeds, but it can be changed by using an overhead camshaft. Therefore, modern sedan engines generally use an overhead camshaft, which is arranged above the engine, shortens the distance between the camshaft and the valve, omits the tappet and tappet of the valve, and simplifies the camshaft to the valve. The transmission mechanism between them will make the structure of the engine more compact. More importantly, this installation method can reduce the reciprocating quality of the entire system and improve the transmission efficiency.

According to the number of camshafts, it can be divided into two types: single overhead camshaft (SOHC) and double overhead camshaft (DOHC). As the mid-to-high grade sedan engine is generally a multi-valve and v-cylinder arrangement, dual camshafts are required. The intake and exhaust valves are controlled separately, so dual overhead camshafts are used by many brand-name engines.