before top dead center - Team Camaro Tech
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post #1 of 4 (permalink) Old Feb 7th, 01, 09:23 AM Thread Starter
Join Date: Feb 2001
Location: greenville ,s.c.,usa
Posts: 3

Is it true that the spark fires and the gas explodes before top dead center? If this is true why does the piston take the path of less resistance and go back down. I can understand the Inertia of the crank and stuff
but on start up you don't have much Inertia

I totally understand the timing thing now
the timing chain is a 2:1 ratio so each terminal is 90 degrees
Thanks to the guys invloved
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post #2 of 4 (permalink) Old Feb 7th, 01, 10:01 AM
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Location: Fortuna, CA
Posts: 26,531

Tony, it's better to keep going in the orig thread than start new ones when it's basically the same topic...

On to your question... Have you ever thrown a football or shot a rifle at a moving target? It's the same thing, you lead the target so that the ball and receiver get to the same spot at the same time.

The spark is triggered btdc so that when the compressed charge is ignited it will push the piston back down at the most effective time. Each motor is different and compression and other varibles effect when you want the spark to fire. Pinging is the result if the spark firing at the wrong time and the piston being fired on too soon or before it reaches TDC. This equates to poor preformance and possible broken parts...

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post #3 of 4 (permalink) Old Feb 7th, 01, 10:26 AM
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As Dennis said, there are many variables that enter into the equation. Let me throw in my .02 here. It takes a certain amount of time for the air/fuel mixture to ignite, burn and expand. It's not instantaneous, so to speak. If you ignited the mixture at TDC, by the time it burned and expanded, the piston would already be on it's way back down.

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post #4 of 4 (permalink) Old Feb 9th, 01, 04:10 PM
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The fuel mixture doesn't "explode" - it "burns"; it takes time for the mixture to ignite, and for the flame front to travel from one side of the chamber to the other and get full expansion of the charge; this is why the spark has to occur earlier in the cycle as rpm increases (more spark advance with increasing rpm).

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