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Thread: What Octane rating?

  1. #1
    Senior Member RACING JUNKIE
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    What Octane rating?

    Just to keep discussion going, We're running a 498" BBC, Dart 360's with roughly 14.7-15:1 comp ratio (SWAG) at high altitudes and bad air (7200'-8600' corrected). I'm thinking 40 to 44 of lead, so where are we at?

    We have a choice of either 112 octane or 116 octane, and the boss and I had a debate about which one we should use. I'm advocating 116 although I think we could get by pretty easy with 112 . . with the ignitions all of us use today, getting it ignited really isn't any kind of a problem . . and at this point, anyway, price really isn't a factor . .

    Just as a reference point, last year we were running a 468 with a lot of leakdown (so compression points really don't come into play), same heads, and used 112 with no obvious problem . .

    I just want to be able to lean on it a little when the air's bad . .

    Discussion?

  2. #2
    Senior Member MASTER BUILDER
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    If your speaking of motor octane and not rated octane 112 will be fine. Alot of fuel companys will have a rated octane and a motor octane which what I have seen they will sticker it as 112 octance and in the fine print it will have 108 motor octane...

  3. #3
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    Whose fuel? There is a huge difference between fuel brands and there octane ratings.

    I would recommend VP Q16 or C12
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    Senior Member RACING JUNKIE TheYellaBrick's Avatar
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    Anyone have a chart showing the octanes of various brands of race gas ?

    I did find this but nothing on race fuel;

    http://en.wikipedia.org/wiki/Octane_rating
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  5. #5
    Senior Member RACING JUNKIE
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    We're looking at Sunoco 116 octane . . and coolracing was pretty close to correct . . "RON" and "Motor Octane" are two different things as are "oxygen content" . . Which, in the case of the latter, DOES change the energy output of a Fuel . . Something that I had been led to believe didn't change with octane ratings in gasoline . . Exactly how much it changes BTU's (Energy output of a fuel) isn't shown on the chart (http://www.racegas.com/fuel/compare) but it has to . . Because that's what "Oxengenated" Fuels do . . BTU's have to change as the burning of the fuel increases/decreases. How much might be another debate . .

    Point is, in our case, we probably need more compression than we currently have, if we're going to run at high altitudes . . Old rule of thumb: "If you have no air, you have to make some" NASCAR whizzes make air in restrictor plate racing by upping the compression in some cases to 17:1 (just one of many of their "secrets") . . But, we also go down to lower tracks sometimes and really can't afford to run two engines . . Christ, it's a bracket car! Sooo, we "Bump the Lead" to up the compression when on the mountain, and back it off a bunch when running below 4800'. Thus, Octane has a lot to do with the up high situation . .

    That's my take on all this, but there's some of you up here who have messed with normally aspirated BBC's a whole lot more than I have . . I'm listening . .

  6. #6
    Senior Member MASTER BUILDER
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    Sunoco i found was one that had a different motor octane rating and alot of people get confused when buying VP fuel due to the fact when they see C12 they beleive its 112 octane awnser is no its 108 motor octane and its good up to a 15:1 c.r. motor. C16 they beleive is 116 octane, the awnser is no its 117 motor octane. I sold race fuel for years and ran into this problem weekly. I advise everyone read the fine print when buying your fuel.

  7. #7
    Senior Member RACING JUNKIE
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    Okay . . FYI . . We've decided on SUNOCO "Maximal Red" . . and according to their chart, it's 116 octane, RON=118 and 114 Motor Octane. with a .708 spec gravity . . kinda light in the density department with their average densities about .745 or so . . But we'll see how it works . .

    Price was right for a 55 at Bandimere's . . . and they had it in stock . .

  8. #8
    Senior Member RACING JUNKIE
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    Quote Originally Posted by roadkill2
    Okay . . FYI . . We've decided on SUNOCO "Maximal Red" . . and according to their chart, it's 116 octane, RON=118 and 114 Motor Octane. with a .708 spec gravity . . kinda light in the density department with their average densities about .745 or so . . But we'll see how it works . .

    Price was right for a 55 at Bandimere's . . . and they had it in stock . .
    how much for the 55?
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  9. #9
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    $577.50, your drum or a $20 drum fee . . That's $10.50 a gallon, or in smaller quantities, $10.65 . . .


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