Adjustable Cam Pulley and how it function?

 Cam pulley is used to rotate the camshaft which in turn will push the valve down.The timing of the valve will depend on the camshaft and the cam pulley.The timing means  when the valve is pushed down. If the valve comes down before the piston reaches its highest point called the top dead center(tdc), the timing is considered ADVANCE.If the valve comes down after the piston reaches  the tdc, it is considered as RETARD. 

Advance Timing

Advance timing means the valve start to come down before the piston reaches the tdc. The advance timing will enhance the lower and mid range of the engine but peak power will be less. This setup is suitable for daly driving in the city where the engine revs at low to mid rpm levels.However if the timing is too advance, it  can cause detonation/knocking/pinging.

Retard Timing

Retard timing in the other hands means the valve starts to come down after the piston has reach its tdc.Retard timing will enhance the high the peak power but sacrificing the mid and low range power. This setting is suitable for drag or racing purposes.