ecu can only adjust the ignition timing for normal engines. for those with vvt or some form of it you can adjust when it happens but not how much.

there are 3 reasons why adjustable pulleys are used.

1 - They just look cool when exposed don't they ?

2 - For engines with out vvt or some form of it, you cannot adjust the cam timing with the standard pulley.

3 - For track guys you will know this. Officially speaking, vvt is something like turbocharging so when on the track there is a weight penalty for cars wif vvt. Thats why the track engines have the vtec disabled or the vvt oil hole plugged.

Don't get mixed up with the ignition timing and the cam timing.

Ignition timing is to adjust when the spark plug fires relative to piston position

cam timing is to control when the valve opens relative to piston position.

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Added on March 1, 2008, 1:38 amalso, the adjusting is actually to suit different the user. If you use the engine mainly at low rpms then less overlap is better. if you are at high rpms more overlap is better.

overlap is the amount of time the intake valve is open while the exhaust valve is open.

This post has been edited by sakaic: Mar 1 2008, 01:38 AM