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Thread: Petrol

  1. #1
    Fellow Frogger! Inspector Clouseau's Avatar
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    Dec 2002
    North Coast NSW

    Default Petrol

    I suspect this might generatye some debate:
    A former army aircraft mechanic blew my concept of the various petrols completely out of yesterday.
    I think this is the summary of his theory- octane is purely a measure of the anti-knock quality of petrol. A petrol that has more octane has less heptane and heptane is what generates the power. So standard unleaded in a motor properly tuned etc should generate more power and efficiency than a high octane petrol.
    Is this so? Does anyone have any info?


  2. #2
    Real cars have hydraulics DoubleChevron's Avatar
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    May 2000



    this is correct. Higher octane only prevents knocking. If you have a high compression motor or turbo'd motor, sure you can get lotsa power out of it on standard petrol, you'll also hole a piston if it pings to badly .... Like everything it's a comprimise.

    eg: i seem to recall deisel actually has the capability of making more power than the same amount of petrol

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  3. #3
    Fellow Frogger! OddFireV6's Avatar
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    Mar 2004


    Octane rating is of course the likelihood a fuel will detonate, LP gas is 110 Octane in Victoria, that’s why my turbo 505 runs on straight gas. I can wind up the boost on a standard compression motor and more than compensate for the lower energy or heat value of Gas in comparison to Petrol.

    A low octane high energy fuel will not work well in a high compression motor, detonation will rob power and eventually damage the engine.

    Higher octane allows you to increase compression and/or turbo boost and derive more power. It’s a fact though that engine power is also proportional the energy value of the fuel and that the energy value of a fuel is not directly related to octane rating.
    504 V6 24V, 203

  4. #4
    1000+ Posts
    Join Date
    Jul 2001
    Perth, Western Australia


    Higher octane fuel actually burns more slowly than lower octane fuel.... Knock happens when the pressure peaks caused by pre-ignition move faster than the speed of sound.

    They've actually both got very similar energy per litre - premium is a liitle bit more dense and therefore stores more energy per litre, but only a tiny bit.


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