Pre igntion is flame initiation prior to spark. Causes are from compression heat, Poor octane fuel, a glowing combustion chamber deposit or overheated tip of sparkplug. Spark knock is from advanced timing, or poor octane. It is caused by early plug spark for that gasoline, or correct timing in low octane fuel. If a flame front is initiated too soon, the trapped mixture is still being compressed as the piston approaches TDC. The heat and pressure of the progressing flame super heat the remaining unburnt fuel/air. this allows it to detonate (combust through its volume all at once, not burn with a flame front. Compare a firecracker to lighting a trail of gun powder with a match) This detonation causes Knock/Ping sound. Modern computer controlled systems listen to each cylinder and adjust timing to produce the tinyest knock. This is not harmful as it is just barely present. The timing thus set produces the greatest Peak pressure in the chamber just as the piston goes past TDC (5 degrees or so), and burns more of the remaining fuel that would normally have quenched out. Todays cars' CPUs learn timing from those sensors and adjust to each cylinder to talior combustion efficience, and adjust for differences between each tank of fuel. Jim
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Today's Featured Article - Chores - by Frank Young. The ceaseless passing of time! It is at once our friend and our enemy. It measures our progress and it makes us old. Like most features of our life, few things are all good or all bad, and most such judgments depend on our own perspective or viewpoint. In our particular hobby, we enjoy the nostalgic return to the days of our youth as we recreate many of the scenes that took place on the family farm that served as the stage for the first few acts of the play that is our live
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