87 vs. 91 octane

Discussion in 'Fiesta ST Chat and Discussion' started by MLKN, Apr 14, 2014.

  1. MLKN

    MLKN Active Member

    Has anyone done any comparison on dyno or otherwise between the two? If there is no appreciable difference I'd like to save a bit on gas. I'd love to hear any educated opinions or just testimonials comparing the two. Thanks.
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  3. wash

    wash Active Member

    If you like slow, you can't beat 87 (unless you can find 85).
  4. MLKN

    MLKN Active Member

    How much slower are we talking here? I realize the trq and hp ratings were with 91.
  5. smatty

    smatty Member

    I've done a tank of 87. It feels sluggish and my gas milage went down a couple mpgs. You aren't saving much per tank by running 87. About $2 a tank?
  6. bryramos

    bryramos Member

    That's my feeling too! Go for 91. It's not that much more, plus your ST will run better. I've only put 91 since it's first full tank from the dealer.
  7. quiznos

    quiznos Member

    91: less chance of knock more chance of unburned fuel (you'll use more) and it'll leave ever so slightly more carbon deposits.

    But I mean. Less chance of knocking.
    I use 93.

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  8. Zormecteon

    Zormecteon Active Member

    It shouldn't knock on the lower octane fuel, as it simply retards the timing using the knock sensor, but the retarded timing means less power.

    I had an '88 Ford Tempo. All I ran in it for years was cheap gas, (ARCO regular). After about 15 years, I put in a tank of Chevron regular. The difference in price was almost exactly equal to the gain in fuel mileage, but the engine was "happier". For the difference in price between regular and premium, in a car equipped as these are, with a knock sensor, my guess is the same effect will occur, but I'm not going to experiment. I'll only ever run premium, if just for the added cleaning package that goes into the higher grade gasoline.
  9. Neely2005

    Neely2005 Member

    What does the Owners Manual say? (The Consumer Reports review says that it takes Regular)

    When I asked my salesman about this he said that all Ford gasoline engines run on 87. He said that running higher octane would only give you an additional 1 or 2 horsepower.

    A couple years ago Consumer Reports did a comparison of Ethanol and Non-Ethanol gasoline and they found that Ethanol gives you a little more power / more horsepower but Non-Ethanol gives you a little better mileage.
  10. Kepz

    Kepz New Member

    I'm no expert, but I don't think octane adds 1-2 horsepower...
  11. ST-in-Mich

    ST-in-Mich Member

    A gas station around the corner from me has 95 octane for the price others sell 93. I try and make it over to that one anytime I need gas,
    quiznos likes this.
  12. MLKN

    MLKN Active Member

    Someone needs to run 0-60 and 1/4 mile times on each and dyno on each. That would be useful data.
  13. Ca5p3r

    Ca5p3r Member

    That's interesting... from my neon (before and after modifying it), Every time that I have found straight gasoline (91 oct or 92 or 93) the car was always happier. noticeable power gains and fuel economy went up by at most 5 mpg. Significant difference to me.

    The owner's manual states that 91 octane is recommended, but it also states that the ST will run on 87 just fine (if you want reduced power and everything).
  14. Neely2005

    Neely2005 Member

    Well Consumer Reports was comparing E85 to gasoline so the differences would probably be less noticeable in regular 87 octane gas as it's only Up To 15% Ethanol.

    Thanks for the information from the Owners Manual. I guess technically my salesman was right when he said that you can run 87 octane.
  15. BlueBomber

    BlueBomber Active Member

  16. quiznos

    quiznos Member

    Ok. Quick explanation. Higher octane = more compression tolerated before combustion due to pressure (knock). More compression before ignition (spark plug) more power.
    Therefore higher octane, higher power, less chance of knock.
    While yes the car will adjust timing (amount of compression before ignition) to avoid knocking you'll lose power. You're also depending on your computer and sensors working correctly every time a cylinder fires instead of pure mechanics and chemistry. Even though miniscule still more of a chance and less power.

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  17. quiznos

    quiznos Member

    Octane Rating - Explained:

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  18. eRic

    eRic Active Member

    ford.com lists the power differences for the 1.6L ecoboost in the Fusion on regular vs premium.
    182 @ 5,700 (premium fuel) 177@5,700 (regular fuel)
    there may be similar differences in the Fiesta ST
    MacDubois likes this.
  19. eRic

    eRic Active Member

  20. MLKN

    MLKN Active Member

    Should be the same as it is the same engine. This answers my question.
  21. Neely2005

    Neely2005 Member

    Octane Recommendations

    1.6L Engine

    Regular unleaded gasoline with a pump
    (R+M)/2 octane rating of 87 is
    recommended. Some fuel stations offer
    fuels posted as regular with an octane
    rating below 87, particularly in high altitude
    areas. Fuels with octane levels below 87
    are not recommended.

    1.0L and 1.6L EcoBoost Engines

    Regular unleaded gasoline with a pump
    (R+M)/2 octane rating of 87 is
    Some fuel stations offer
    fuels posted as regular with an octane
    rating below 87, particularly in high altitude
    areas. Fuels with octane levels below 87
    are not recommended. Premium fuel will
    provide improved performance and is
    recommended for severe duty usage such
    as trailer tow.

    Do not be concerned if your engine
    sometimes knocks lightly. However, if it
    knocks heavily while you are using fuel with
    the recommended octane rating, see an
    authorized dealer to prevent any engine

    Last edited: Apr 22, 2014

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