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  1. #51
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    rate of burn depends on fuel composition and doesn't really relate to octane. Most engines these days are designed to increase burn rate. Octane is more autoignite temp and cylinder cooling. The reason E85 (or any fuel) is more effective with DI is that all the vaporization happens in the cylinder raising the effective octane. If a fuel vaporizes in the manifold the combustion cooling effect has been mostly wasted. All these threads recently on E85 octane being 95AKI or so, fail to mention that octane is measured in a carburated test engine, so the results are meaningless really. Your increased MBT results are due to effective octane. E85 mixes allow you to get closer to optimum peak pressure of 15ish deg ATDC, but pump gasoline would be limited by detonation... do some testing with race gas. I've also seen some studies that methanol, ethanol detonation is much more violent then gasoline.

    Your EGT studies will be interesting, but make sure you do it on a dyno cause you can over advance on e85 which would look great on the EGT measurement, but not so good for the engine.

    Sorry, I don't have any sources to site... just mull over different forums, papers and try and decide what's accurate... and of course the not so accurate brain thinking.

  2. #52
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    Click here to enlarge Originally Posted by JoshBoody Click here to enlarge
    I do NOT think a slower burn rate really has any "positive" effects on an engine. Increases likelihood of detonation and reduces mechanical advantage. A slower burn rate would have a higher average energy per time...
    I'm not sure but this is just what I have heard. Higher octane will have a slower burn rate and there is a point where you can have too much octane with negatives due to slow burn rate.

    However, there is a point up to where the slower burn rate of higher octane (although it differs with different fuels) helps somewhat. Just what I've heard not sure if correct.

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  4. #54
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    ^ Ok so when people say too much octane regarding burn speed... they are wrong?

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  5. #55
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    ^ Ok so when people say too much octane regarding burn speed... they are wrong?
    I don't think octane is directly correlated to burn speed. Within one fuel - say 87, 89, 91, 93 - it very well may be. But it is not necessarily true across all fuels. So, yes, sometimes it may be, especially for some fuels (say gasoline), but it isn't always.

  6. #56
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    Click here to enlarge Originally Posted by rudypoochris Click here to enlarge
    So, yes, sometimes it may be, especially for some fuels (say gasoline)
    So does it hold true for gasoline?

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