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This is a discussion on Premium vs Regular: The octane thread within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Originally Posted by Speedette Side note: do you think you'd see the same increase when using 93 octane versus 96-100 ...

  1. #16
    Registered User jcaputo's Avatar
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    Quote Originally Posted by Speedette View Post
    Side note: do you think you'd see the same increase when using 93 octane versus 96-100 octane (race gas)?
    Quote Originally Posted by Micah View Post
    If the ECU isn't tuned for it, I don't think there would be much benefit other than a better resistance to detonation from the higher octane.
    That's what I was thinking. There should be essentially no change running higher octane on a stock car.

    That's actually why I was curious about the 91 octane versus the 93. There may be more savings to be had if the engine doesn't detonate using 91, and there may be no noticeable difference between 93 and 91.

    I don't have my owner's manual in front of me, anyone know what it actually recommends? Is it 93 or 91?
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  3. #17
    Resident meany-rator 06wrx4me's Avatar
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    Quote Originally Posted by jcaputo View Post
    I don't have my owner's manual in front of me, anyone know what it actually recommends? Is it 93 or 91?
    WRX recommends 91 oct Sti recommends 93. Nicely done
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  4. #18
    Registered User efmd3's Avatar
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    don't forget that generally, higher octane fuels have less energy, but can be more efficient at burning them.

    meaning (i think) if you put 93 in a car tuned for 87, you will get worse gas mileage, but if you tune it for 93 (compression/boost) it can get close to and possibly better gas mileage.

  5. #19
    Registered User Micah's Avatar
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    grain of salt without numbers

    Quote Originally Posted by efmd3 View Post
    don't forget that generally, higher octane fuels have less energy, but can be more efficient at burning them.

    meaning (i think) if you put 93 in a car tuned for 87, you will get worse gas mileage, but if you tune it for 93 (compression/boost) it can get close to and possibly better gas mileage.
    What is the actual % difference in energy between octane ratings.

    Anyone have numbers on this.
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  6. #20
    Registered User efmd3's Avatar
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    Quote Originally Posted by Micah View Post
    What is the actual &#37; difference in energy between octane ratings.

    Anyone have numbers on this.
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    Typical fuel energy contents:
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    1 gallon methanol = 62,800 Btu
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    (10% ethanol, 90% gasoline) = 120,900 Btu
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    (85% ethanol, 15% gasoline) = 90,500 Btu
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    Last edited by efmd3; 05-13-2008 at 12:20 PM.

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    Quote Originally Posted by Trainrex View Post
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    Quote Originally Posted by 20WRX04 View Post
    Nice write up.
    Quote Originally Posted by wrx wagone View Post
    Nice work!
    Indeed.
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    Geriatric Ginger Mod Rogan's Avatar
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    Quote Originally Posted by 04.SPT.WRX View Post
    ... hidden away from others ...
    was he in that basement, for 24yrs?

    Nice test, though..

    I did something like this a few years ago, just never posted it.
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  9. #23
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    89 vs 91

    using a low grade fuel will cause a ping and will cause damage to ur pistons, i have seen it so try to plus staying with one grade of fuel is better for ur car.

  10. #24
    Geriatric Ginger Mod Rogan's Avatar
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    Quote Originally Posted by subytech209 View Post
    using a low grade fuel will cause a ping and will cause damage to ur pistons, i have seen it so try to
    isnt "ping" just another name for the more disastrous sounding "DETONATION"..? Yes.



    Posted octane numbers on gasoline pumps are a result of testing fuel performance under laboratory and actual operating conditions. The higher the octane rating on fuel the less volatile (evaporative qualities) and the slower the fuel burns. Higher octane fuel contains more POTENTIAL energy but requires the higher heat generated by higher compression ratio engines to properly condition the fuel to RELEASE that higher potential energy. In the refining process, fewer gallons of higher octane fuels are yielded from a barrel of raw crude, thus the higher cost. If fuel octane is too low for a given compression ratio, the fuel prematurely and spontaneously ignites too early and the fuel charge EXPLODES rather than BURNS resulting in incomplete combustion. The net effect is a loss in power and possible engine damage. The operator hears an audible "knock" or "ping", referred to as detonation. Detonation may vary from a faint noise on light acceleration to a constant, deep hammering noise while driving at a constant speed. Improper timing adjustments, vacuum leaks, or excessively lean fuel mixtures may also cause detonation. - excerpted from WikiAnswers



    plus staying with one grade of fuel is better for ur car.
    ..wut??
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  11. #25
    Registered User teflon_jones's Avatar
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    Here's another interesting experiement:
    What happens if you use 91 octane in a stage 2 STi with a 93 octane OTS Cobb map?

    Absolutely nothing.

    Why would you want to do this? I just haven't gotten around to loading the 91 octane map on the ECU after moving from Mass to Colorado. Maybe tomorrow...
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  12. #26
    Registered User pacemaster's Avatar
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    Thumbs up Octane..

    Thanks for this great info..
    There were a couple of contradictions....though.
    Someone said [detonation] with 87 octane..the ecu doesn't compensate enough?? or does it.. worse milage is great info running 87. Better milage with 93-- where i live at 5000 feet only 91 is available.. maybe 89 is fine at high altitude? Or run the hightest octane i can get and get the best mpg's possible?
    Owned my 06 Rex for two weeks and liking it alot. 23k k on it.

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    I must say I do truly enjoy the fact that you went into full details thank you very much for the info... team 93 haha

  14. #28
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    Quote Originally Posted by YB_WRX_2013 View Post
    I must say I do truly enjoy the fact that you went into full details thank you very much for the info... team 93 haha
    Nice bump and great search (I'd think) on your part.
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  15. #29
    Registered User Ingo's Avatar
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    ...and yes, at higher altitude the octane numbers don't need to be quite that high, hence there is only max 91 octane available in Colorado. At lower altitude there is usually higher octane available and should be used. When I took a road trip to Iowa I had that and didn't see any problem. As stated repeatedly, the higher consumption of lower grade fuel plus the danger of causing harm makes it not worth going with lower grade fuel. Back then my wife was not aware that it takes premium - she would have nixed the WRX in a heart-beat. But then it was too late, and she got used to it since. I still have respectable MPG's (20 in city) and that's ok (compared to 20 with regular in a Suzuki sidekick).
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    E85!!!!!

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