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Thread: 4AC carby with 98 octane

  1. #1
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    hi, i'd like to know the advantages and disadvantages of running 98 octane fuel ina 4ac. is anyone owning a 4ac and running 98 octane, if so what do u think about it

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    Site Supporter Javal's Avatar
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    <div class='quotetop'>QUOTE (orange 86 @ Feb 17 2008, 04:41 PM) </div>It will run stronger, cleaner and not detonate.

    You can crank some more timing into it too for a smidge more go.
    You can have any brew you want... as long as it's a Datsun / Corolla / What is that?

  3. #3
    gunbz-r
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    will definately run smoother and may not ping, but the power increase will be barely noticeable, if u can notice it all, and before flamage begins, did the power u felt from ur pod filter start in the seat of ur pants, or in ur head?

    unless u have plenty of money, i wouldn't bother, think about the extra 15c per litre, then think about how cheap a ge is

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    Veteran Jonny Rochester's Avatar
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    If the motor has relatively low compression, the 98 octane will make almost no difference.

    But as people have said, try using it and advance the timing a bit. Will make performance slightly crisper, if you notice it.

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    you feel better when you valve bounce it

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    Veteran Jonny Rochester's Avatar
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    You are so right! Valve bouncing does have a strange therapeutic nature.

    Feeling down? Lost your girlfriend? Try valve bouncing a 4A-C along a twisty highway.

  7. #7

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    My 4AC pings on hot days, well even mildly warm days, with 91. 98 stops that. No noticable power difference. My girlfriend now can identify pinging and has a basic understanding of it too.

    Hen

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    whats valve bouncing?

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    Senior Member orange32's Avatar
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    from my understanding its a phenomenon when the valve springs cannot keep up with the revolutions from the camshaft and they 'bounce'. Not very good for an engine, but the 4ac loves it!

    I missed a gear once and revved mine to 7.5K with no valve bounce... is that normal? Its a FWD 4ac :ph34r: ... don't ask

    On topic: I've always run my car on 98 octane as i thought it needed it, i think i'll only run it on track days now and 91 for street driving.

  10. #10
    Member ronin_SPL's Avatar
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    I ran BP 98 RON in my 4k and even with the timing advanced to about 13 degrees there is no pinging and it definitely makes it smoother.

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