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Elevation changes, octane ratings.

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  • Vaquero

    Moving stuff to the gas prices thread.....
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    Apr 4, 2011
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    Dixie Land
    We're headed to 8000' elevation soon.
    Starting at 1200'.
    Ram 1500 5.7 hemi 2015 model.
    Towing a travel trailer.
    Once we get to Lubbock, all "regular" fuel will be 86 octane.

    Question....
    Will a higher octane rating on the last leg of ascension be beneficial?
    I'm not well versed on the air/Fuel mix stuff.

    TIA.
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    Kar98

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    The opposite is true: higher elevation states sell regular with lower octane ratings. Colorado regular is 85, instead of 87 in Texas, and you'll be fine using that. Higher elevation = less air = less early detonation ("knock")
     

    avvidclif

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    I'm guessing the computer in your truck will take care of all that for you. It can sense altitude and check for knock and adjust accordingly. That truck is way smarter than you think.
     
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    HK
    I'm guessing the computer in your truck will take care of all that for you. It can sense altitude and check for knock and adjust accordingly. That truck is way smarter than you think.


    You are correct. The ECM will adjust the fuel map, ignition timing to adjust for the thinner air. It won't matter what octane is in the tank.
     

    BRD@66

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    So (as an example), if I gas up in San Angelo w 86 proof, my ECM will make that weak crap run ok when I get back to Austin?
     

    Kar98

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    First, you need to learn that octane rating has got nothing to do with power. It's a measurement of the gasoline's ability to resist engine knock. Higher octane denotes greater knock control.

    Typically, the engine's computer will detect engine knock and adjust timing and the air/fuel ratio accordingly. Although this protects the engine from damage, it can substantially reduce engine performance and efficiency.

    Most high-compression gas engines require use of premium gas to better resist engine knock and prevent the computer from detuning the engine to protect against knock-related damage. Using premium gas in a clean, mechanically sound engine not designed to use it, though, provides no benefit.

    In
     

    ZX9RCAM

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    Typically, the engine's computer will detect engine knock and adjust timing and the air/fuel ratio accordingly. Although this protects the engine from damage, it can substantially reduce engine performance and efficiency.

    Most high-compression gas engines require use of premium gas to better resist engine knock and prevent the computer from detuning the engine to protect against knock-related damage. Using premium gas in a clean, mechanically sound engine not designed to use it, though, provides no benefit.

    In

    This is what I was talking about.

    Down on power.
     

    ZX9RCAM

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    Right. So the lower rated octane will make no difference at higher altitude, and for the 50 miles of driving around lower altitude one gets out of half a RAM 1500 tank, it will cope. ;)
    Yes, it will cope, but be "down on power" for the reasons you stated above .
     

    TxStetson

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    If his 5.7 Hemi is anything like the one I used to drive, using more gas would have you walking after 500 yards. It was fast, it could pass anything but a gas station. 11mpg and a 20 gallon tank. That put me stopping for gas twice on my way to Oklahoma.
     

    Kar98

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    Is that because it's down on power and requires more throttle to move like you're used to?




    :green:

    It's because the fuel/air mixture it expects is different than the one it gets and the timing is out of whack. Higher octane gas is not "richer in energy".
     

    ZX9RCAM

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    It's because the fuel/air mixture it expects is different than the one it gets and the timing is out of whack. Higher octane gas is not "richer in energy".

    Never said, or implied this.

    As you already stated, power is down due to retarded timing as the octane is lower .
     

    Sock Puppet

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    If his 5.7 Hemi is anything like the one I used to drive, using more gas would have you walking after 500 yards. It was fast, it could pass anything but a gas station. 11mpg and a 20 gallon tank. That put me stopping for gas twice on my way to Oklahoma.

    Measured in gallons per mile?
     
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    HK
    High octane is a slower burning fuel. Lower octane is faster burning. In performance applications. You want an explosion at the very beginning of the valve timing. With it burning slower to cover an amount of time.

    Lower octane treated the same way causes a different explosion. Faster. You can use it for advantage when you need the pop to happen later in the timing. Earlier in timing and it'll cause knocking.

    My camaro is programmed for 93. It'll run like $hit on 87. Unless I refresh the computer to time for 87. Then no problems besides lower horsepower. The camaro is specific for octane.

    The dodge is too. 87. Only that. High altitude means thinner air mixed with the same fuel. It causes a softer explosion. It might feel a little sluggish.
     
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