Timing - educate me
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From: Madison WI
Timing - educate me
Okay, well as much as I know about cars/engines I must admit timing is a field I don't know much about at all. Does anyone have a paper or any links that will explain to me the specifics of timing, i.e. initial timing vs. timing @ x RPM, timing curves, effect on power output, etc. etc.? It's really something I would like to learn about. Thanks for any help in advance 
Racer
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From: Washington DC
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Joined: Sep 2004
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From: Madison WI
Thanks a lot for the link - it'll definitely come in handy.
What I'm looking for right now is more an explanation of timing itself and what initial timing is vs. timing at a certain rpm, and the effects on power output of all this...
What I'm looking for right now is more an explanation of timing itself and what initial timing is vs. timing at a certain rpm, and the effects on power output of all this...
Racer
Joined: Dec 2005
Posts: 344
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From: Washington DC
oh man. ok...
timing refers to the point in the stroke of the piston in which the spark plug actually fires, igniting the gasoline. the initial timing is how far before top dead center the plug fires when the engine is at idle (usually 6-14ish degrees before the top of the stroke).
since the constant in this system is the gasoline combustion time, it is necessary to ignite the gasoline sooner in the stroke to make sure the gasoline burns soon enough to generate maximum power.
so, as the rpms increase, the plug spark will become more advanced to accomodate the speed of the engine. this is accomplished by weights in the distributor that are pulled by centrifugual force as their rotational velocity increases. this moves the timing to its full advance (usually 32-38ish degrees before the top of the stroke).
there is also vaccum advance in there which kicks the advance up in relation to the vaccum signal coming from the engine.
thats about the most simplistically i can describe it. i am sure others can chime in with specific tuning and power info. hope this helps...
timing refers to the point in the stroke of the piston in which the spark plug actually fires, igniting the gasoline. the initial timing is how far before top dead center the plug fires when the engine is at idle (usually 6-14ish degrees before the top of the stroke).
since the constant in this system is the gasoline combustion time, it is necessary to ignite the gasoline sooner in the stroke to make sure the gasoline burns soon enough to generate maximum power.
so, as the rpms increase, the plug spark will become more advanced to accomodate the speed of the engine. this is accomplished by weights in the distributor that are pulled by centrifugual force as their rotational velocity increases. this moves the timing to its full advance (usually 32-38ish degrees before the top of the stroke).
there is also vaccum advance in there which kicks the advance up in relation to the vaccum signal coming from the engine.
thats about the most simplistically i can describe it. i am sure others can chime in with specific tuning and power info. hope this helps...
Thread Starter
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Joined: Sep 2004
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From: Madison WI
Originally Posted by mensch53
oh man. ok...
timing refers to the point in the stroke of the piston in which the spark plug actually fires, igniting the gasoline. the initial timing is how far before top dead center the plug fires when the engine is at idle (usually 6-14ish degrees before the top of the stroke).
since the constant in this system is the gasoline combustion time, it is necessary to ignite the gasoline sooner in the stroke to make sure the gasoline burns soon enough to generate maximum power.
so, as the rpms increase, the plug spark will become more advanced to accomodate the speed of the engine. this is accomplished by weights in the distributor that are pulled by centrifugual force as their rotational velocity increases. this moves the timing to its full advance (usually 32-38ish degrees before the top of the stroke).
there is also vaccum advance in there which kicks the advance up in relation to the vaccum signal coming from the engine.
thats about the most simplistically i can describe it. i am sure others can chime in with specific tuning and power info. hope this helps...
timing refers to the point in the stroke of the piston in which the spark plug actually fires, igniting the gasoline. the initial timing is how far before top dead center the plug fires when the engine is at idle (usually 6-14ish degrees before the top of the stroke).
since the constant in this system is the gasoline combustion time, it is necessary to ignite the gasoline sooner in the stroke to make sure the gasoline burns soon enough to generate maximum power.
so, as the rpms increase, the plug spark will become more advanced to accomodate the speed of the engine. this is accomplished by weights in the distributor that are pulled by centrifugual force as their rotational velocity increases. this moves the timing to its full advance (usually 32-38ish degrees before the top of the stroke).
there is also vaccum advance in there which kicks the advance up in relation to the vaccum signal coming from the engine.
thats about the most simplistically i can describe it. i am sure others can chime in with specific tuning and power info. hope this helps...
Thanks again! If there's anything you want to go into more detail about, feel free
Last edited by 72Tornado; Apr 17, 2006 at 08:01 PM.
Melting Slicks
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From: Madison Ms
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There is an excellent article in the most recent edition of Corvette Fever Magazine on Timing. It is a good read.
Instructor
Joined: Apr 2006
Posts: 174
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From: Wallaceburg Ontario
Damn it, ignition timing confuses the HELL outta me. I can't understand why a plug would be set to fire BEFORE top dead centre. If the piston is still on it's way UP, wouldn't it be fighting against the explosion that's trying to push it back down? In my scientifically-challenged mind, it would make more sense for the gas/fuel mixture to detonate AFTER top dead centre; in other words, when the piston has just begun it's trip back DOWNWARD. 
Racer
Joined: Dec 2005
Posts: 344
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From: Washington DC
Originally Posted by Chilli
Damn it, ignition timing confuses the HELL outta me. I can't understand why a plug would be set to fire BEFORE top dead centre. If the piston is still on it's way UP, wouldn't it be fighting against the explosion that's trying to push it back down? In my scientifically-challenged mind, it would make more sense for the gas/fuel mixture to detonate AFTER top dead centre; in other words, when the piston has just begun it's trip back DOWNWARD.
If you were to ignite the gasoline AFTER the top of the stroke, the piston would already be on its way down by the time gasoline burned. It would also not be compressed and you would not generate any power.
The constant here is the time it takes to burn the gasoline. If the engine is running at 800 or 8000 rpm, the gasoline doesnt burn any faster. That is the reason for the advance in a distributor. Since the piston is moving faster, you have to start the ignition of the gasoline sooner in the stroke to make sure full combustion is happening just as the piston hits the top of the stroke.
Is that any clearer, Chilli?
Racer
Joined: Dec 2005
Posts: 344
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From: Washington DC
Here is another good explanation (with pictures!)
http://auto.howstuffworks.com/ignition-system1.htm
http://auto.howstuffworks.com/ignition-system1.htm
Le Mans Master
Joined: Jan 2006
Posts: 8,319
Likes: 7
From: Wilmington DE, Drive it like you stole it, 68 327 4 speed coupe
Originally Posted by mensch53
oh man. ok...
timing refers to the point in the stroke of the piston in which the spark plug actually fires, igniting the gasoline. the initial timing is how far before top dead center the plug fires when the engine is at idle (usually 6-14ish degrees before the top of the stroke).
since the constant in this system is the gasoline combustion time, it is necessary to ignite the gasoline sooner in the stroke to make sure the gasoline burns soon enough to generate maximum power.
so, as the rpms increase, the plug spark will become more advanced to accomodate the speed of the engine. this is accomplished by weights in the distributor that are pulled by centrifugual force as their rotational velocity increases. this moves the timing to its full advance (usually 32-38ish degrees before the top of the stroke).
there is also vaccum advance in there which kicks the advance up in relation to the vaccum signal coming from the engine.
thats about the most simplistically i can describe it. i am sure others can chime in with specific tuning and power info. hope this helps...
timing refers to the point in the stroke of the piston in which the spark plug actually fires, igniting the gasoline. the initial timing is how far before top dead center the plug fires when the engine is at idle (usually 6-14ish degrees before the top of the stroke).
since the constant in this system is the gasoline combustion time, it is necessary to ignite the gasoline sooner in the stroke to make sure the gasoline burns soon enough to generate maximum power.
so, as the rpms increase, the plug spark will become more advanced to accomodate the speed of the engine. this is accomplished by weights in the distributor that are pulled by centrifugual force as their rotational velocity increases. this moves the timing to its full advance (usually 32-38ish degrees before the top of the stroke).
there is also vaccum advance in there which kicks the advance up in relation to the vaccum signal coming from the engine.
thats about the most simplistically i can describe it. i am sure others can chime in with specific tuning and power info. hope this helps...
Racer
Joined: Dec 2005
Posts: 344
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From: Washington DC
Originally Posted by sweethence
Hey mensch good for you, seemed like just yesterday you were asking what a distributor was
Le Mans Master
Joined: Jan 2006
Posts: 8,319
Likes: 7
From: Wilmington DE, Drive it like you stole it, 68 327 4 speed coupe
Originally Posted by mensch53
Haha. Thanks. If you pulled my distributor, took it completely apart, threw the parts in a box and told me to get the car running again, I would probably have some problems. But, I can point to it, do an electronic module swap, set the timing, and tell you what it does - all things I definitely could not have done 3 months ago
aw c'mon you'd be surprised, I bet you could do it lickey split
you've got two stars now lot to live up to 
Last edited by sweethence; Apr 18, 2006 at 02:06 PM.
Drifting
Joined: Sep 2004
Posts: 1,959
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From: North Bend Ohio
Originally Posted by Chilli
Damn it, ignition timing confuses the HELL outta me. I can't understand why a plug would be set to fire BEFORE top dead centre. If the piston is still on it's way UP, wouldn't it be fighting against the explosion that's trying to push it back down? In my scientifically-challenged mind, it would make more sense for the gas/fuel mixture to detonate AFTER top dead centre; in other words, when the piston has just begun it's trip back DOWNWARD.
If the mixture reacted in the same way explosives do your engine would last about 3/4'th of its first, and only, revolution. BOOM!
BigBlockk
Later.....
Instructor
Joined: Apr 2006
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From: Wallaceburg Ontario
Originally Posted by mensch53
Is that any clearer, Chilli?
Pro
Joined: Jun 2005
Posts: 725
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From: FL.
Higher octane ratings come into play because its desireable for the fuel air mix to burn smoothly all over the top of the piston, Not explode on it. So the higher the octane rating the longer the burn the more power in the stroke.
