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. The advance/retard is measured by degrees for example advance 2ｰor retard 2ｰ.
The adjustable cam pulley, as the name implies, it means the pulley is adjustable.as for the adjustable cam pulley (acp), the timing can only be set at one position/angle and can only be changed when the engine is not running.

100% Brand New, Really High Quality
Come with total of 2 cam gear.
- Color: purple/Red/Blue/Yellow,etc.
- Accurate Adjustments: +/- 20 Degree
- True Laser-Etched Markings On The Leading Edge Of the Gea
- High quality grade 10.9 heavy steel bolts used for long life expectancy
- Decrease shift time and length.
- Reduce shift throw for 45%-50%
- Will make custom timing possible for high performance cams and modified engines
- Direct stock replacement.
- TO Install by professional mechanic