Optima SX: FUEL GRADE vs MPG
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Thread: Optima SX: FUEL GRADE vs MPG

  1. #1
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    Optima SX: FUEL GRADE vs MPG

    Has anyone noticed better fuel economy with a higher fuel octane ?

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    01/2012 ROTM securityguy's Avatar
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    The engine is designed to run on 87 octane. Anything more is not only a waste of money but can cause problems due to the increased octane. Higher octane does not coincide with higher mpg.
    Last edited by securityguy; 09-05-2011 at 09:42 PM.
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    Thanks !

    Reason Im asking is bcoz someone another thread stated that they were achieving about 35 mpg (60 % city / 40 % highway) while running on 93 octane.

    My assumption was that turbo engines would run more efficiently on a higher octane although it's not required for the SX.

    Any thoughts anyone ?

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    Quote Originally Posted by rockwell View Post
    Thanks !

    Reason Im asking is bcoz someone another thread stated that they were achieving about 35 mpg (60 % city / 40 % highway) while running on 93 octane.

    My assumption was that turbo engines would run more efficiently on a higher octane although it's not required for the SX.

    Any thoughts anyone ?
    Look up gdi ..dif than fuel injection ..sort of like a diesel. I have tried several tank fulls of both 87 and 91 octane for weeks at a time. Still averaged 427-440 a tank regardless of octane...just a though.

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    Octane rating (as I recall) only indicates a tendency to resist pre-detonation or "engine knock." More highly tuned cars require this resistance by design, but the Kia engineers were nice enough to tune for 87 and not advance our timing so much as to require it.

    If I am wrong, please correct.

    Of course as soon as an aftermarket software company changes the tuning and requires 93 we should also be getting a few more ponies out of our optimas. I am guessing somewhere around 310-330 depending on what they do to boost levels.

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    Tuning will be of little difference concerning the octane required. The compression on each cylinder is low and by design does not require high octane gas.

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    Quote Originally Posted by crystalworks View Post
    Octane rating (as I recall) only indicates a tendency to resist pre-detonation or "engine knock." More highly tuned cars require this resistance by design, but the Kia engineers were nice enough to tune for 87 and not advance our timing so much as to require it.

    If I am wrong, please correct.

    Of course as soon as an aftermarket software company changes the tuning and requires 93 we should also be getting a few more ponies out of our optimas. I am guessing somewhere around 310-330 depending on what they do to boost levels.
    Quote Originally Posted by Avgwarhawk View Post
    Tuning will be of little difference concerning the octane required. The compression on each cylinder is low and by design does not require high octane gas.
    ^ This.

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    Quote Originally Posted by securityguy View Post
    The engine is designed to run on 87 octane. Anything more is not only a waste of money but can cause problems due to the increased octane. Higher octane does not coincide with higher mpg.
    Not correct. Higher octane fuel will have no impact whatsoever
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    Senior Wrench Monkey NJ OSX's Avatar
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    Quote Originally Posted by Avgwarhawk View Post
    Tuning will be of little difference concerning the octane required. The compression on each cylinder is low and by design does not require high octane gas.
    War,
    maybe I'm stuck in old school but you'd call 9.5:1 low compression?
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    Quote Originally Posted by NJ OSX View Post
    War,
    maybe I'm stuck in old school but you'd call 9.5:1 low compression?
    I'd agree and even call that low...compared to the cars post 1972, when 8.2-8.5:1 was considered the new "high", anything less than 10.2 is low to me.
    I believe the determining factor is the mfg's recommendation for fuel. Seems anything under 10:1 today uses 87.
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