Re: A 'What is' and 'What does it do' question!

[geordy <grostad@thresholdnetworks.com>]

I was saying that I tweaked the ignition timing and felt a powerband change.
So that is infact just my imagination then?

Jonas Karlsson wrote:

>> 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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