How does higher octane reduce pinging?

Discussion in 'The Garage' started by Nacho, Jan 6, 2007.

  1. Nacho

    Nacho Active Member

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    I know pinging is unburnt spark. And I also know that advancing the timing makes your spark spark quicker which can cause pinging if not using higher octane fuel. My question is, how or why does higher octane reduce pinging? I know it takes more to ignite which reduces pinging, but I don't know how it does that. I also know that if you use higher octane on a car that doesn't need it, power is lost, but I just can't explain to myself why higher octane reduces pinging, please explain. :'(
     
  2. ryclef331

    ryclef331 Well-Known Member

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    Ok this might take a bit....stay with me.


    Pinging is NOT "unburnt spark." Pinging can be described as either detonation or spark knock. Two different things actually. I'll explain octane first.


    Octane is a measure of how "fast" the fuel burns or it resistance to combustion. The higher the number, the more "stable" or resistant to ignition it is. How does this help or hurt you when timing a vehicle? Well, when you time your ignition, you want the MOST pressure built up and ready to start pushing that piston back down on the power stroke. This also makes the burn sequence last long for a more complete burn and the most power. Make sense? SO you actually START the ignition sequence EARLY before the piston reached absolute top dead center....the piston is still compressing the fuel and air when the spark plug actually fires. Now, if you have a fuel that has a lower octane rating (i.e. burns FASTER), it can actually burn TOO FAST after the SPARK PLUG FIRES and try to push the piston back DOWN while it is still trying to come UP and finish the compression stroke. That is why you want to run a higher octane fuel when advancing the timing. THAT is SPARK KNOCK.

    Now Detonation is pre-ignition. The fuel and air actually ignite before the spark plug even fires. This is detonation NOT spark knock. BOTH sound exactly the same but alot of times detonation is caused by alot of things. Too much compression for your fuel's octane (boost also), spark plugs are too hot of a heat range, hot engine parts (valves and piston faces), etc. ALL can cause detonation. WHen you compress something it gets HOT. When you're compression an already unstable mix of fuel and air, too much isn't always the best. The compression of the intake charge can get so great that it heats up to the point of igniting. WHen this happens before the spark plug was supposed ignite it, this AGAIN, tries to push the piston BACK down on its compression stroke.

    Detonation, pinging, preignition, spark knock...whatever you call. ALL are the quickest way to a blown motor...HANDS DOWN no matter how built it is.

    I hope that explains it.
     
  3. Dalamar

    Dalamar Legend Retired Staff SN95 Supporter

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    Great answer Ryclef!
     
  4. 94darkhorse

    94darkhorse Legend

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    Very detailed!
     
  5. exactly!

    I'll have to put this in the tech on the website
     
  6. ryclef331

    ryclef331 Well-Known Member

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    Glad to help.
     
  7. Olstangguy

    Olstangguy New Member

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    Whew ! Ryclef331 Great post, Best explaination i've ever seen on the subject
     
  8. Nacho

    Nacho Active Member

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    Thanks a lot Ryclef! Explained it to perfection and easy to understand. O0
     
  9. CanaryGT

    CanaryGT Well-Known Member

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    Great Writeup!