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87 vs 91 (or 92) Octane?

I've always believed that if 87 octane is specified by the manufacturer, then you're wasting money to use 91 or higher. However, recently a friend sent me the following link regarding a serious test using a dynamometer that indicates otherwise.

http://www.europeancarweb.com/tech/proven/epcp_1007_2010_volkwagen_jetta_proven/- viewall.html

I sometimes drive my 2011 Honda Fit Sport 5M really hard on nearby twisty mountain roads, constantly accelerating (with all its mighty 117 horses) to red line. So I plan to put in a couple of tankfuls of 91 octane (as high as it gets around here), to see if I can feel a difference.

Now, what do you think, and why?
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Comments

  • I'd say it's generally a waste of $ to spring for the higher octane stuff. However, if you're running the piss out of the thing which causes it to run hotter than nommal, then it may be worth something.

    You can usually hear if you're getting detonation (a pinging / knocking noise). If you notice this while running hard, you may want to spend the extra $ on higher octane.
  • bhill2bhill2 Posts: 1,333
    This brings up an interesting question. In the bad old days, a car designed for higher octane (premium) gas would suffer from destructive detonation if run on lower octane (regular) gas. Conversely, a car designed to run on lower octane gas did not benefit from using the higher octane.

    However, with the modern engine management systems, most (or all) cars designed to run on higher octane gas can run on a lower octane with diminished performance but no damage.

    The question is, do some (or even all) cars designed to run on the lower octane gas have the capacity to benefit from a higher octane? If some but not all, which ones have this capacity? Finally, if such cars exist, how do they differ from the ones designed to run on a higher octane gas but able to use the lower octane gas?

    2009 BMW 335i, 2003 Corvette cnv, 2001 Jaguar XK cnv, 1985 MB 380SE (the best of the lot)

  • andysdandysd Posts: 87
    The original posting has received two replies, but no one has watched or commented on the video that was the reason I started this thread. The video is an objective search for the real answer, not just opinion, including dynamometer curves, to learn whether the conventional viewpoint is valid that there is no benefit to using higher octane gas than specified by the car manufacturer.

    I do know that using lower octane in a Mercedes can cause damage. When I had one, a '94 C280, I heard a service guy explain that to a customer, showing her a carbon-encrusted internal engine part he kept on his counter.

    Someone, please watch the video: http://www.europeancarweb.com/tech/proven/epcp_1007_2010_volkwagen_jetta_proven/- - viewall.html

    Just copy and paste it to go to that location.
  • bhill2bhill2 Posts: 1,333
    edited December 2011
    Actually I did watch the video (well I read the text; I didn't realize that it was a video.) In fact, that test, which showed a Jetta which specified 87 octane fuel performing better on 91 octane, was the genesis of the questions that I posed in message 3.

    2009 BMW 335i, 2003 Corvette cnv, 2001 Jaguar XK cnv, 1985 MB 380SE (the best of the lot)

  • andysdandysd Posts: 87
    Hi bhill2 -

    Sorry, yes, I see the point in your last para of Reply 3, and I forgot it was only text and graphs. I know the 5-cylinder VW engine isn't a barnburner - even my Fit has a better 0-60 time - so maybe it's the sort of under-stressed engine that would benefit from higher octane.

    I bet a lot of people won't accept that there would be any improvement to engines specified for 87. In fact, I'm still on the fence.

    Today, I ran my Fit hard in the mountains starting with a full tank 50% 91. It felt great but it always does. Now I'll run it to near empty, fill up with 91, and get a seat of the pants impression.

    In the other direction, I special-ordered new a '99 Z28 that I still have. The manual specifically says it's ok to use 87 with lower h.p. I phoned the GM techs to be sure. Since I don't need all that h.p., I've been using 87 in it for years, getting 30.2 mpg door to door San Diego-Indianapolis-San Diego because sixth gear is 1,750 at 75 mph. Engine is in great shape with about 65k miles. But if the manual required premium gas, I'd never use regular.
  • robr2robr2 BostonPosts: 7,760
    Sometimes an engine can benefit from using higher octane than required/recommended but it is rare AFAIK.

    For instance, my 05 Passat with the 1.8T requires a minimum of 91. Around here, 93 is common so that's what I use. If I were to run 89 or lower, the computer would compensate for that which results in lower MPG.

    My 00 Odyssey states in the manual that if one were to use 91 isntead of the recommended 87, the HP will increase from 200 to 205. I've used premium a few times in the van and to be perfectly honest, I couldn't feel the difference.

    IIRC, C&D did an article on this a few years ago in which they did their road and dyno tests to see if there was a benefit of using premium in vehicles rated for regular. The results were there was not a benefit.
  • fintailfintail Posts: 33,561
    edited December 2011
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    Not going to use regular even if the car might somehow compensate for it. "Only" means something, especially to finicky engineers.

    image

    Old car gets the good stuff too, even if I am tempted to run my homemade gasoline-benzol-alcohol mixture :shades:
  • andysdandysd Posts: 87
    edited December 2011
    12-12-2011 Update: Now the gas in the tank of my 2011 Honda Fit is all 91 octane. It certainly seems more powerful by seat of the pants; I don't give full gas as much; it seems to pull better at full throttle high rpm; seems more tractable at low rpm; and the fuel consumption gauge seems to have jumped 10% from 30 to 33 mpg. Not scientific observations but I am tending to believe it helps.
  • steverstever YooperlandPosts: 40,147
    You might accomplish the same thing (assuming anything is really different :shades: ), by putting regular "pure gas" in. (pure-gas.org)

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  • andysdandysd Posts: 87
    Good thought. I would if I could, but only 5 such stations in CA, far from me.
  • fezofezo Posts: 9,328
    As always there isn't a station with a couple of hundred miles from me that sell the good stuff.
  • steverstever YooperlandPosts: 40,147
    Funny, I'm in the boonies with not all that many stations and the third nearest one is ethanol free.

    I never buy it, but it's available. Maybe because of the boaters though.

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  • I see the same thing on my 2010 Honda CRV. It runs better on 93 Octane gas and gets better fuel economy on trips. It's underpowered as it is, and, using premium gas helps.

    Regards:
    Oldengineer
  • andysdandysd Posts: 87
    to Oldengineer from a very old engineer (87 next month).

    I started this thread with the link to the objective study using a dynamometer and the 5-cylinder VW engine. You are the first to confirm what I think I'm seeing - more power and better mileage, in my case with a 2011 Honda Fit Sport 5mt on 91 octane - and corroborating the premise. I'd have to revert to 87 octane to see whether the mpg meter drops back, because my engine is still pretty new at 4,000 miles, and break-in might be a factor.

    I plan to write a letter to the editor of Car & Driver magazine on this subject because they published the first article I've seen that recognized the Fit's sports driving merits, surprising them with its result in the emergency lane change test, going 6 mph faster than any other car including Ferrari F430, Corvette Z06, etc. Am hoping they'll explore both the 87 vs higher octane question, and the stock Fit as a GT performer on twisty roads. A race-prepared Fit (with stock engine and transmission) has already proven itself on the race track, e.g., in the 2010 25 hour Thunderhill race where the C&D entry placed 15th overall, lapping at 83 mph. I put 17-inch Kosei Racing wheels with 215/45 Kumho SPT's (left over from an '04 Civic) on mine, and run very well with real sports cars on San Diego East County's great winding two-lane mountain roads. Am hoping C&D will explore this aspect of sport driving the stock Fit, possibly enhanced by the 91 octane theory. It would be valuable to see whether they can also confirm the theory by a dynamometer.
  • oldbearcatoldbearcat Posts: 170
    edited December 2011
    I bought the 2010 CRV to use as a business driver. It has 60K on it now. After I broke it in, I was really disappointed with its fuel economy. My other little SUV, a Mercedes GLK 4Matic will easily match the CRV's fuel economy on long trips at interstate speeds and absolutely blow its doors off. I discovered that the CRV has a relatively high compression engine - which led me to try 93 octane gas. Overall, it seems to improve the fuel economy about 3 MPG on long trips, makes the car feel a bit more peppy, and eliminates a bit of hesitation I get if I'm heavy on the throttle. By the way, I'm 65.

    Regards:
    Oldengineer
  • robr2robr2 BostonPosts: 7,760
    Overall, it seems to improve the fuel economy about 3 MPG on long trips, makes the car feel a bit more peppy, and eliminates a bit of hesitation I get if I'm heavy on the throttle.

    Does the added mpg offset the added expense of premium though?

    Does it make a difference during in-town driving?
  • andysdandysd Posts: 87
    edited December 2011
    Consensus seems to be growing! Another believer.

    Three of us have seen indication of about 10% improvement in fuel mileage. Californiagasprices.com indicates a 6% difference in gas prices, so a 10% improvement in mpg definitely would pay off. Then there's the bonus of the indicated tractability improvement at lower rpm - that sort of relates to your question about in-city driving.

    I was considering putting premium in my 2011 Honda Accord SE, but I have no interest in more horsepower, and it runs so smoothly on regular, that I haven't so far. However, in the interest of science, maybe I will - if only to see if economy is improved. Yesterday's fill-up showed 25.5 mpg with primarily city driving.

    Oldengineer brought out the relationship between compression ratio and likelihood of benefit. Before I started this thread, I emailed back to the friend who first sent me the link about the European test,

    "It might make even more difference on the SV [my Suzuki SV650 motorcycle], which has a high compression ratio of 11.5.

    "The Fit's is 10.4, and the Jetta 2.5 L's is 9.5, so it might benefit the Fit more than the Jetta, because the Fit might be closer to pinging."

    I hope C&D will take up an accountable study of the matter (if I ever get around to writing them).
  • robr2robr2 BostonPosts: 7,760
    IMHO, the results seen are by no means scientific. Butt-o-meter readings and mpg over different conditions doesn't really prove anything.

    If you can show actual results in a controlled environment, they'll I'll start to believe.

    BTW, my Passat requires premium. I paid a 12% premium for it today.
  • steverstever YooperlandPosts: 40,147
    "Premium, in fact, sometimes is worse fuel than regular. It resists knock because it's harder to ignite than lower-octane fuels. As a result, some engines won't start as quickly or run as smoothly on premium, notes Gibbs, the SAE fuel expert.

    No data show that engines designed strictly for regular run better or longer on premium. "

    Why use premium gas when regular will do?USA Today)

    To quote Mr. Shiftright, premium gas is not a doggie treat for your car. :)

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  • andysdandysd Posts: 87
    1. Seat of the pants indications are qualified as such. The goal is to have another test accountable by dynomometer like the European test referenced in my original posting.

    2. No one is suggesting to use regular where premium is specified, just the opposite.

    3. How could you pay a 12% premium? I just checked Californiagasprices.com which shows $3.29 avg low price for regular, mostly at Arco, and $3.49 for premium. that's a difference of 6%.
  • andysdandysd Posts: 87
    I agree you are quoting the prevalent viewpoint, but contrary to your statement, there are data that indicate differently. Please read my original posting, and check out the referenced link:

    #1 of 21 87 vs 91 (or 92) Octane? by andysd
    Nov 25, 2011 (1:23 pm)
    I've always believed that if 87 octane is specified by the manufacturer, then you're wasting money to use 91 or higher. However, recently a friend sent me the following link regarding a serious test using a dynamometer that indicates otherwise.

    http://www.europeancarweb.com/tech/proven/epcp_1007_2010_volkwagen_jetta_proven/- - viewall.html

    I sometimes drive my 2011 Honda Fit Sport 5M really hard on nearby twisty mountain roads, constantly accelerating (with all its mighty 117 horses) to red line. So I plan to put in a couple of tankfuls of 91 octane (as high as it gets around here), to see if I can feel a difference.
  • steverstever YooperlandPosts: 40,147
    edited December 2011
    I remember the first post. :shades:

    Dyno results are more persuasive than seat of the pants stuff. Even then, the linked results aren't spectacular by any means, nor will real world conditions mimic the dyno test conditions very often. We're talking peak power gain of 7 hp @ 5790 rpm and peak torque gain of 13 lb-ft @ 4150 rpm. The torque number is interesting, but the HP number at those rpms is practically a rounding error. I'm not sure how they got 7 hp subtracting 133 from 138 for test 1 either. :shades:

    So I want to see your dyno numbers. :)

    Btw, that link of yours breaks, probably because of the dashes - here it is for those wanting to see it.

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  • robr2robr2 BostonPosts: 7,760
    3. How could you pay a 12% premium? I just checked Californiagasprices.com which shows $3.29 avg low price for regular, mostly at Arco, and $3.49 for premium. that's a difference of 6%.

    I pulled into a Mobil today here in Boston. 87 was priced at $3.45 and 93 was priced at $3.85. That's 11.59% more.

    Although the price spread typically is only $0.20 between 87 and 93, I've noticed more stations jacking up 93 by more. I think it's because the stations understand that some buyers have to use premium whereas folks like you can switch to regular without any issues.
  • robr2robr2 BostonPosts: 7,760
    Btw, that link of yours breaks, probably because of the dashes - here it is for those wanting to see it.

    I followed that link and read the story. There is a mention of a $300 intake in the middle of it without reference to the story. Does this have anything to do with it?
  • andysdandysd Posts: 87
    At least in the San Diego area, 91 is the highest generally available. There must be cars like yours around here. Are you sure your owner manual's requirement won't be satisfied with 91 if that's available in your area?
  • andysdandysd Posts: 87
    I'm sure you can interpret the intake question as well as I. Am going to try to spend less time on this, and try to write C&D about their doing the test including dyno we all want.
  • steverstever YooperlandPosts: 40,147
    As I read it, they put the intake on to further increase the hp and torque and called it Test 2.

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  • andysdandysd Posts: 87
    You mention compression ratio as a possible factor. I agree, and in reply to someone else who touched on c.r., I replied:

    Dec 14, 2011 (9:42 am)
    Consensus seems to be growing! Another believer.

    Three of us have seen indication of about 10% improvement in fuel mileage. Californiagasprices.com indicates a 6% difference in gas prices, so a 10% improvement in mpg definitely would pay off. Then there's the bonus of the indicated tractability improvement at lower rpm - that sort of relates to your question about in-city driving.

    I was considering putting premium in my 2011 Honda Accord SE, but I have no interest in more horsepower, and it runs so smoothly on regular, that I haven't so far. However, in the interest of science, maybe I will - if only to see if economy is improved. Yesterday's fill-up showed 25.5 mpg with primarily city driving.

    Oldengineer brought out the relationship between compression ratio and likelihood of benefit. Before I started this thread, I emailed back to the friend who first sent me the link about the European test,

    "It might make even more difference on the SV [my Suzuki SV650 motorcycle], which has a high compression ratio of 11.5.

    "The Fit's is 10.4, and the Jetta 2.5 L's is 9.5, so it might benefit the Fit more than the Jetta, because the Fit might be closer to pinging."

    I hope C&D will take up an accountable study of the matter (if I ever get around to writing them).
  • robr2robr2 BostonPosts: 7,760
    At least in the San Diego area, 91 is the highest generally available. There must be cars like yours around here. Are you sure your owner manual's requirement won't be satisfied with 91 if that's available in your area?

    My VW will run on 91 but it's not readily available in the northeast. The only brand that offers it is Sunoco and there's only one that I know of.

    Around here it's 87, 89 and 93.
  • andysdandysd Posts: 87
    I get you. Too bad. Better move to SD; the weather's better, too.
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