Adjustable Cam Pulley. Advance or Retard The Timing

What is cam pulley? Cam pulley is used to rotate the camshaft which in turn will push the valve down. The timing of the valve will depend on...

What is cam pulley? 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, the timing is considered ADVANCE. If the valve comes down after the piston reaches the top dead center, it is considered as RETARD.

The advance/retard is measured by degrees for example advance 2°or retard 2°. The adjustable cam pulley, as the name implies, it means the pulley is adjustable.This will allow the valve timing to be changed and this is how the VVTi system works, but VVTi system depends on the engine speed and it it is changed while the engine is running. However for the adjustable cam pulley, the timing can only be set at one position/angle and can only be changed when the engine is not running.

So why we need adjustable cam pulley? This is because different timing is needed for different speed of engine (rpm) to get the most efficient combustion.The cam pulley can be adjusted to suit the driving style of the driver. The powerband of the engine can be shifted by varying the timing of the valve.

Basically there are 2 types of settings. One is the advance timing and the other one is the retard timing. So let's talk about them.

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.

Buying the Cam Adjustable Pulley

There are several brands in the market, for example: HKS, Arospeed, Works and Jasma. Before  you getting one of them, you must know that whether there is any marking for the advance and retard and whether crankshaft timing or the camshaft timing.

Here are the lists based on what I know off,
1. HKS - There are Advance and Retard marking on the cam pulley and it is refering to the Camshaft Timing.

2. Arospeed - There are Advance and Retard marking on the cam pulley and it is refering to the Crankshaft Timing.

3. Works - There are Advance and Retard marking on the cam pulley and it is refering to the Crankshaft Timing.

4. Jasma - There are NO Advance and Retard marking on the cam pulley. If you get this set of cam pulley, it is very difficult for the tuner to set the timing. So better get other brand and always remember, cheap does not means good in car performance.

Here is the example picture of what I mentioned above. Noticed the red circles compare both the Jasma cam and HKS cam.

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