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Thread: 87 vs 91 octane

  1. #1
    deepcolor is offline Registered Member What I drive: Genesis 4.6 V8 Tau Sedan
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    Default 87 vs 91 octane

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    ok, w/ gas prices soaring (4.29 for regular where i live and 4.50 for premium) at the pump and no end to these high prices in the near future, what are you guys using?

    i have always used premium (91 octane) but now i'm considering 87.
    just wondering if you will feel a difference in the accelleration and power.

    i had a little better than a half of tank of premium and accidently topped it off (7.5 gallons) w/ regualr 87 octane. i thought i noticed a difference in acelleration and power w/ a slight pause / hessitation when trying to accellerate, but that could be psychological i guess.


  2. #2
    frankv64's Avatar
    frankv64 is offline Registered Member What I drive: Genesis 5.0 V8 R-Spec Sedan
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    Default Re: 87 vs 91 octane

    You are saving $4.00 in a tankfull, does it really matter? Maybe if you fill up every other day
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  3. #3
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    scottdk is offline Registered Member What I drive: 1G Genesis 4.6 V8 Tau Sedan
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    Default Re: 87 vs 91 octane

    Quote Originally Posted by frankv64 View Post
    You are saving $4.00 in a tankfull, does it really matter? Maybe if you fill up every other day
    What he said ^
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    homeofstone is online now Registered Member What I drive: Genesis 4.6 V8 Tau Sedan
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    Default Re: 87 vs 91 octane

    I don't understand those that buy 30k and up cars having a problem with high gas prices. If gas seems expensive at 3 for or even 7 dollars a gallon and you are driving a new $30,000 then maybe a small used economy 40mpg car was more in order.(saves on tax, insurance and tires too)
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    PMCErnie is offline Registered Member What I drive: 1G Genesis 3.8 V6 Sedan
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    Default Re: 87 vs 91 octane

    Interesting. One sincere, honest, question and three putdown answers.

    Deep Color, why not try a couple of tanksfull of 87, or 89, and see for yourself?
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    TJPark01 is offline Registered Member What I drive: 4.6 V8 Tau Sedan
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    Default Re: 87 vs 91 octane

    Run both and see if you can tell a difference. I couldn't tell the difference, so I just use 87. However, I can tell the difference on cold start up using Mobil 1 0W-20 advanced fuel economy.
    4.6 Platinum Metallic/Black

  7. #7
    fazerG8R is offline Registered Member What I drive: Genesis 3.8 V6 Sedan
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    Default Re: 87 vs 91 octane

    High compression engines make a lot of power because they're high compression engines, not because they burn high octane fuel. They need high octane fuel to prevent pinging (or knocking). With modern ECU's and oxygen sensors, flow meters on air and gas, ping detectors, etc. controlling the fuel air mixture and cam and ignition timing, you're really stretching it to say you're going to outguess the factory engineers that set up the entire package. Put in what the owners manual says to. Simple as that. This question is like the one surrounding using nitrogen to fill the tires, but that's another thread.

    What does Hyundai say to feed the 4.6?

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    scottdk is offline Registered Member What I drive: 1G Genesis 4.6 V8 Tau Sedan
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    Default Re: 87 vs 91 octane

    Quote Originally Posted by fazerG8R View Post
    What does Hyundai say to feed the 4.6?
    87 Octane

    or

    91 or higher octane for another 7 HP.

  9. #9
    fazerG8R is offline Registered Member What I drive: Genesis 3.8 V6 Sedan
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    Default Re: 87 vs 91 octane

    I'd love to see the dynomometer curves for the 4.8 on both fuels. The ping sensor seems to allow a more aggressive timing wih the high octane fuel, allowing a higher power output. I wonder if the higher output is only available at full throttle, or if there's a progressive input. Which fuel is used is going to be determined by the guy driving, and what they feel is giving them the "best" performance for the $$'s.

    I guess that I'd go for the 87 if I lived in Florida and did a lot of steady state interstate crusing, and use the 91 if I lived in the mountains and really needed a lot of full throttle response.

    Good topic.

  10. #10
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    427435 is offline Registered Member What I drive: Genesis 5.0 V8 R-Spec Sedan
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    Default Re: 87 vs 91 octane

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    Running premium fuel will allow the engine to run with a little more advance and provide 3-6% better mpg. That pretty well wipes out the higher price.

    While the engine may run OK with regular fuel, it will be running with some detonation (it takes some detonation for the knock sensors to kick in and retard the timing). Detonation is like smoking cigarettes----------you may be fine for a while, but the damage usually catches up with you.

    Bottom line, the cost difference (if any) vs the possible internal problems makes it stupid to run 87 octane fuel. This from an engineer that has been an SAE member and engine nut for over 45 years.
    Mark

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