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I'm confused about advancing timing and what it does

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I'm confused about advancing timing and what it does

 
Old 08-03-2001, 02:08 PM
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Larry82
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Default I'm confused about advancing timing and what it does

So, am I right that if you advance the timing, the plugs fire earlier that they would otherwise? if so, does this mean that they are firing before the full charge of fuel has been delivered as happens without advancing timing? If so, is this a less efficient burning of the fuel? (so, is that why retarding results in better burning and less emissons).

Some give me a primer on advancing the timing, please! :confused:
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Old 08-03-2001, 02:28 PM
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Chris Fowler
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Default Re: I'm confused about advancing timing and what it does (Larry82)

I'm definitely interested to hear this one too. :bigears
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Old 08-03-2001, 03:16 PM
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Default Re: I'm confused about advancing timing and what it does (Larry82)

An ideal engine would not have timing for the spark plug to fire when the piston is at TDC or even before it gets there (advanced), but when the piston rod is at a 90 angle with the axis of the crankshaft so that the lever arm of the thrust can be maximized and the air/fuel mixture to be burned instantaneously to fill the chamber with a complete charge of steam and all of the energy from that steam be exhausted at that point. This won't work though cause the air/fuel mix doesn't burn instantaneously and the crankshaft is spinning so not all of the air/fuel mix will be burned.

To compensate for the properties of a real engine timing is set so that all of the air/fuel mix is burned by the time the piston reaches TDC so there is a full head of steam through the entire length of the power stroke. If the crankshaft was at a standstill then timing would be set just a hair past TDC, but as the crankshaft begins spinning timing needs to be set more advanced cause it takes time for the air/fuel mix to be completely burned...at around 700RPM (idle) timing is around 8 and needs to be increased as RPMs increase to allow more time for the air/fuel mix to burn. One of the problems with this is there will be steam BTD which exerts a force against the rotation of the crankshaft and works against the direction we want the piston to travel...and at some point RPMs will turn the crank so fast that proper timing so that all the air/fuel was burnt before TDC would cause too much energy from the steam to be transferred to the engine before TDC resulting in insufficient energy for the power stroke and a reduction of HP from the engine...not to mention :smash: extreme stresses in the power train resulting it blown head gaskets, bent or broken rods, burned pistons, etc.

The reason it takes more time for the air/fuel mix to burn is the spark ignites the air/fuel mix and the flame must travel throughout the chamber to get in contact with all the molecules of the air/fuel mix. To compensate...an additional spark plug can be inserted into the combustion chamber at a different point to reduce the distance the flame needs to travel by half...you will see this in high-performance fuel heads...all of the top fuel dragsters and funny cars have two MSD ignition kits for their two spark plugs. Platimum coating in the combustion chamber will also speed up air/fuel mix burning...all that is offered is just a platinum tip on spark plugs, but a chamber and piston top with an electroplated platinum coating would improve performance by a great deal and allow RPMs to reach greater levers without destruction from internal stresses. :cheers:
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Old 08-03-2001, 03:27 PM
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Default Re: I'm confused about advancing timing and what it does (Rockn-Roll)

Wow! It kinda makes sense when you put it that way. :D

thanks!
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Old 08-03-2001, 04:25 PM
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Larry82
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Default Re: I'm confused about advancing timing and what it does (Chris Fowler '80)

What I said!

Seriously, that is what I thought. Point to me is that if you advance too far, you do fight against the compression and actually loose power.

This is also consistent with premium fuel being a slower burning fuel, I think, so that on hi-po motors you can have timing advanced and have fuel still burning through the compression stroke.

I guess, in layman's terms, that explains detonation, in that timing too advanced, or octane too low (too fast burning) so that burn cycle is through, mostly, before compression finishes, giving sort of a shock wave? Right?
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Old 08-03-2001, 05:09 PM
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Paul L
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Default Re: I'm confused about advancing timing and what it does (Larry82)

I have pinging on hard acceleration. I use Sunoco 94. If I understand correctly then I should back off from the factory setting of 12btdc to 8-10 to compensate for the less volatile fuel. :confused:
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Old 08-03-2001, 05:59 PM
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Default Re: I'm confused about advancing timing and what it does (paul79)

No, when you have a higher RON, thus slower burning fuel you will have to advance the timing some more. This because the flame front will travel slower, if you retard the timing (or leave it the same) the piston will be down further in the bore before the burning is completed.

Marck
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Old 08-03-2001, 06:24 PM
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Larry82
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Default Re: I'm confused about advancing timing and what it does (Twinnie)

Not that I would ever question you, :yesnod:, if you have to go to higher octane fuel in you have detonation, and/or, you normally retard to eliminate detonation, wouldn't you reduce advance if you are already at peak octane? I mean, don't they work hand in glove - low compression/stock timing, low octane and high compression/advanced timing, high octane.
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Old 08-03-2001, 06:44 PM
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Default Re: I'm confused about advancing timing and what it does (Larry82)

Advancing or retarding the idle (initial) timing is not the full answer to elininate detonation or increase available power. You can change the weight springs in the distributor to change the rate of mechanical advance. For example, if you have detonation at 4500 rpm and mechanical timing is full in, you would retard the intial a bit. But if your mechanical is still coming on at that point it would be time to change the springs. Never overlook the rate at which the vacuum advance comes on and drops away for WOT either. Must folks have their mechanical advance full in at 34-36 degrees at around 2600-2800 rpm.
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