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Info for newbs - what is ignition timing and knock?

Discussion in 'General Automotive Discussion' started by [email protected], Nov 20, 2016.

  1. Hello,

    I figured I would try to help people understand what Ignition Timing actually is.

    So, I want you to imagine a cylinder in constant rotation with the crank shaft.
    Cylinder goes down = Air fills cylinder
    Cylinder Comes up = Compression + Ignition
    Cylinder Goes Down = Power
    Cylinder goes back up = Exhaust

    With this being said:
    Ignition timing is the amount of degrees that the Crank is at when the spark is ignited to light the fuel.

    So, What you want in order to optimize power is for the Ignition to occur slightly before TDC (Top Dead Center; Reference to when the Piston is at 0deg). This means that you want the spark to ignite everything just before the piston reaches 0deg. so when the piston is starting to push up the combustion needs to occur that way the force of the piston will compress the combustion and force the piston down harder.

    General Rule of thumb: Ignition needs to occur 10-30deg before TDC (This gives time for compression and rebound to push the crank in the correct direction)

    Knock! Knock! = This happens when you have an Irregular detonation this will happen shortly before the "Optimal" point for ignition. If your piston is on its way up and the combustion happens too early this will create a knock.. Maybe not literally but, if you could be inside your engine you would understand. The pressure of the combustion forcing its piston down before it could ever reach TDC then it will push against the crank versus with the crank.

    I do hope that this helps some people understand what Knock actually means, and maybe increase some general knowledge about how the Internal Combustion Engine works.

    If you have any comments that could help people understand you are encouraged to do so. With the type of performance we all chase knowing all of this information is essential.

    I will probably be creating more threads about these "General" informative threads!

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  2. Great post with good info. Knock, Knock....one of the scariest things ever to a car enthusiast.
  3. This is true! You have to keep an eye on that!
  4. AndersS

    AndersS Lurker

    Great post and good described.:)
  5. Knock not to be confused with rod knock, ie bent rod causing audible knock. Could knock cause rod knock?
  6. DirtKurt

    DirtKurt Private Vendor

    Rod knock is different than knock, or detonation. Rod knock is caused by a wiped out rod bearing. But yes, pre ignition can lead to spun rod bearings, broken pistons and bent rods.