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Re: A 'What is' and 'What does it do' question!
>From: "David" <DavidMac@Btinternet.com>
>What is the advance and retard?
>What does it do?
Those words have to do with Timing. Confusion is caused by the fact that
there is Ignition Timing and Valve Timing.
Most commonly discussed is ignition timing. The ignition distributor is
basically a stationary cap and a rotating rotor (along with vehicle specific
housings, etc.) The rotor is spun by the motor, and it makes contact with
the leads on the cap, by loosening the distributor housing, you can turn the
stationary cap a bit, and adjust the time at which the spark is distributed
to the spark plug. For VW's the spec is 6degrees Before Top Dead Center
(BTDC). You can get more power out of the motor by advancing it a little
more (up to 12degrees BTDC). The problem arises with too much advance. This
causes pre-ignition (AKA detonation, AKA pinging, AKA knock). Basically the
air-fuel charge is ignited non-uniformly, and extreme pressure shockwaves
are created. Shortens life of heads, headgaskets, piston rings, and rod/main
bearings. Eventually the motor will be damaged.
The second kind of timing is Valve timing. The valves are opened and shut by
the camshaft. The camshaft is in turn rotated by the timing belt. You can
buy an adjustable cam sprocket that allows you to turn the cam without
turning the timing belt. This allows you to change the timing of the valves.
By advancing the timing (i.e. the valves open and shut earlier) the
powerband is shifted down in the RPM range. This is great for daily driving,
but Bad for racing. Retarding the valve timing will increase the power at
high RPM, but you lose it down low. This is great for race cars that spend
the whole race at 5500-7000 RPM, but sucks for stop-n-go traffic.
Hope I don't offend anyone by going back to the basics. If I did, too bad.
:-)
Jonas
85 Scirocco 2.0
78 Scirocco 1.8
87 Scirocco 16V
For direct reply: jonas@metabolex.com
http://www.geocities.com/scirocco2l8v
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