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fuel , compression and knock ?s

Discussion in 'General Tech and Maintenance' started by law195, Jun 8, 2004.

  1. law195

    law195 Junior Member

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    I'm trying to figure this ping thing out. IS ping or knock when you have to much or too little fuel in the cylinder. As far as i can put together it's when the compression gets too high and the mixture pre ignites. Is that the same as desiel then just not controlled? And then how does fuel octane work into the picture. does higher octane mean it can take higher or lower CR and what arre the other benefits of going with a higher octane fuel. Sorry but i'm just trying to get it all together at once cuase there is so much i'm confused :blink:
    thanks for the help.
     
  2. stuntstere

    stuntstere Member

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    on my friends car when he uses a 87 octane his car knocks and then when he puts in the 92 octane it stops. the higher the octane the fuel is the better it burns
     
  3. Import R

    Import R Senior Member

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    Detonation is when your flame front, caused by your spark plug igniting, does not impact your piston uniformly. Detonation can also be caused by a lean air/fuel mixture. Pre-ignition is not the same as detonation. Pre-ignition is caused by a hot spot inside your cylinder which prematurely ignites the air/fuel mixture well before the spark plug was intended to fire. Both will cause what people defer to as "ping" and "knock". If your car is equipped with a knock sensor, it is constantly "listening" for knock/ping. When it finds it, it will gradually retard your timing to try and get rid of it. This will eventually lead to your CEL coming on to alert you to the problem.

    As far as your fuel mixture and octane ratings...

    A lean (more air, less fuel) mixture is likely to cause detonation. A rich (more fuel, less air) is likey to bog down your engine and decrease your gas milage. What stuntstere said about higher octane fuels buring better is semi true. A more correct statement would be to say that higher octane fuels are more resistent to knock than lower octane fuels. Most nitrous and turbo kits will tell you to run 93 octane. If you ran regular 87 octane, you would be more likely to detonate. There was a wonderful FAQ I read about the differences in octane ratings, how they get them, and what's best for your setup. Older cars that have higher amounts of carbon deposits in their engines will also benefit from using 93 octane to help deduce the risk of detonation and pre-ignition, but these are generally cars that are 10 years old or more. If I can find the link to the site I found about the octane ratings, I will go ahead and post it up. You might wanna run a search and see if somebody has already posted it in the past.

    Hope this helped out a little.
     
  4. sleepercivic

    sleepercivic Senior Member

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    higher octane burns slower= less chance of detonation

    knock sensor will only through CEL if the sensor is damaged or you have bad wiring, otherwise it will just retard timing if it detects knock
     
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