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Thread: Octane ? how high or low

  1. #1
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    Octane ? how high or low

    I've read alot where people use way more octane than they really need because a lot of them think that the more octane the faster, and I know thats not true so other than making passes and and going with what runs the best is there a formula that you can go by like compression or what. like what needs 112 or 114 or 116 or maybe I only need 110. I use 114 because the man I bought the car from said thats all he used, but down here around Houston no tracks carry 114 we all mix 112 and 116.
    anyway is there a Formula, Thanks Andy

  2. #2
    Senior Member RACING JUNKIE
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    Do not run more octane than you need.

    Dave
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    "All that is necessary for the triump of evil is for good men to do nothing" Edmund Burke

  3. #3
    Senior Member RACING JUNKIE
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    Quote Originally Posted by oldandtired
    Here is a rough recomendation. I have left out the lead count, the aromatic hydrocarbon content and specific gravity. There is also a difference in burning speed, energy value and cooling effect.
    PM me if you want it all.

    105 octane, CR under 12.5 to 1
    108 octane, CR under 14.0 to 1 (75% of all racing engines)
    114 octane, high CR and 8500+ rpm (comp cars)
    116 octane, high CR and high RPM (ProStock, comp eliminator)
    117 octane, Turbo and blown applications

    Dave
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    "All that is necessary for the triump of evil is for good men to do nothing" Edmund Burke

  4. #4
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    That is some good info Dave, My engine is a sbc 434- 15.33 to 1 compression, so maybe 112 would be all I need. thats what I ran in my 421 @ 14.5 to 1 and it did good, What is the ill efects of running to much Octane. I still have a lot to learn and I just want to be right,
    Thanks Andy

  5. #5
    Senior Member RACING JUNKIE
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    Andy, I think 112 would be correct, if it's measured MON.

    MON is octane rated as Motor Octane Number.
    RON is measured as Research Octane Number (ususlly rated higher)
    PON is the combination divided by 2 (R+M/2) and is what you see at the gas pump.

    The highest rating a fuel can have is 120.3.The highest octane fuels burn slower therefore they will not detonate at compression rations of 18 to 1.



    Dave
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    "All that is necessary for the triump of evil is for good men to do nothing" Edmund Burke

  6. #6
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    Running too lower octane can cause detonation because it will ignite at a lower temperature. Too higher octane will run like crap because its not all burning or igniting properly.
    It Ain't Over Til Its NOVA - 634ci of S*#t Your Pants!

  7. #7
    Senior Member RACING JUNKIE
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    112 is fine, we did some testing a few years back with fuel 110/112/114 on a 900hp 555 it liked 110 and no signs of detonation, most said it needed 114
    David Lanning
    IHRA NHRA 387B

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  8. #8
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    Thank you David. I think I'm going to try that 110 and the 112 and see what this thing does. I'm going out tonight to test my new trans brake Solenoid and switch out so I'll do the gas also. and thank yall again,
    Andy

  9. #9
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    well the 114 must had been to much. I have never ran below 6.20 in the 1/8 and tonight I ran a 6.10 a 6.15 and a 6.11 after I went down on the Octane from 114 to 112 Thats hard for me to believe but its a fact, my 60' times went from 1.42 to 1.38 so now I believe I may try 110 next week and see what happens. Thanks guys for the information and help on this.
    Andy Byrd

  10. #10
    Senior Member MASTER BUILDER
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    How did the transbrake go?
    It Ain't Over Til Its NOVA - 634ci of S*#t Your Pants!


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