By on December 14, 2017

Most readers of this site know exactly what an octane rating is and how it relates to the bang it provides in an engine. Hauling up to the pumps and being presented with a choice of everything from 87 to race gas is one of the benefits of living in America.

Higher octane fuel is more expensive than other grades and the gulf between regular and super-duper-extra premium is steadily increasing. Is it worth “treating” your car to a tank of high octane every now and then? The American Automobile Association says absolutely not — and they have the testing to back it up.

For its tests, AAA used 87-octane (regular) and 93-octane (premium) gasoline in six vehicle models varying in body style, size, type of fuel delivery system and air induction system. Each vehicle was identified as a model that the manufacturer recommends the use of premium gasoline. All gasoline used for testing was EPA Tier III certification fuel with 10 percent ethanol content in both regular and premium octanes. Certified test fuel was used to remove variability in fuel quality and additives. Each vehicle was tested on a dynamometer.

The organization does allow that premium gasoline provides a benefit in select vehicles. Vehicles such as high-strung supercars need the extra octane in order to run optimally and produce the advertised amount of horses.

“AAA’s testing reveals that drivers could see modest gains in fuel economy and performance when opting for premium gasoline in vehicles that recommend, but do not require, the higher-octane fuel,” said Megan McKernan, manager of the Automobile Club of Southern California’s Automotive Research Center. “Those seeking the maximum capabilities of their performance-focused or utility vehicle may see some benefit from using premium gasoline, particularly over the long haul.”

Makes sense. Only the most tinfoil-hatted paranoid android would believe a random engineer deep within the bowels of an OEM would slap a “Premium Recommended” sticker on a car simply because they’re getting kickbacks from Big Oil. To prove a point (and settle many arguments fought in garages since the invention of premium unleaded), AAA strapped test gear to a few cars and came up with some quantifiable results.

In a fit of real-world usability, the association published the exact make and models they used in the test, along with exacting results. From the report:

  • Fuel economy for test vehicles averaged a 2.7 percent improvement. Individual vehicle test result averages ranged from a decrease of 1 percent (2016 Audi A3) to an improvement of 7.1 percent (2016 Cadillac Escalade).
  • Horsepower for test vehicles averaged an increase of 1.4 percent. Individual vehicle test result averages ranged from a decrease of 0.3 percent (2016 Jeep Renegade) to an improvement of 3.2 percent (2017 Ford Mustang).
  • According to national averages, the price difference between regular and premium gasoline is approximately 20 to 25 percent, or 50 cents per gallon.
  • The modest fuel economy improvements found in AAA tests do not offset the higher cost of premium gasoline.

The 7.1 increase increase in the Escalade is interesting, until one remembers their learnings in basic math. At 15 mpg, that percentage increase works out to a single mile per gallon. In the A3 cited in the story, a 1.0 percent drop in economy would bring a 28 mpg performance down by approximately a quarter of a mile per gallon.

Those numbers are averages of results taken while testing those machines on four different simulated road gradients. The Caddy recorded its biggest increase in economy on flat terrain at 65 mph, jumping from 23.3 mpg to 26.4 mpg. This points to the cylinder deactivation technology benefitting greatly from the good stuff. A 6-percent grade at 55 mph saw an increase from 10.73 mpg to 11.02 mpg. The other testing parameters were a 2-percent and 4-percent hill taken at 65 mph.

Horsepower results are even more interesting. The study cites usage of a naturally aspirated 2017 Mustang equipped with the 5.0-liter V8 and an automatic transmission. Ford rates this engine at 435 crank horsepower, noting “premium fuel” in parenthesis. Check out AAA’s dyno results:

AAA Premium Fuel Study

The organization used six vehicles in its testing: a rear-wheel drive 2017 Ford F-150 with the 3.5-liter EcoBoost and 10-speed automatic, a Cadillac Escalade equipped with its fabulous 6.2-liter V8 and eight-speed auto, a stickshift 2015 Mazda Miata, a non-quattro Audi A3 with the six-speed dual clutch autobox, a 5.0-liter Ford Mustang automatic, and a row-your-own MultiAir-equipped Jeep Renegade.

The full report, all 68 pages of it, can be found here.

[Graph: AAA]

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77 Comments on “Won’t Get Fueled Again: AAA Testing Suggests Premium Gas, for the Most Part, Isn’t Worth Your Cash...”


  • avatar
    Hoon Goon

    Send me link to your part out thread if you run 87 octane in a turbocharged 4 popper for the long term. Especially an older one with less complex knock control strategies.

    • 0 avatar
      Steve65

      Just as soon as you find one of those which doesn’t require premium…

      • 0 avatar
        Delta88

        Volkswagen recommends 87 octane on the 1.4T and 1.8T as seen on the stickers affixed to the fuel door (some fine print in advertising and a blurb in the owners manuals recommends 91 octane to guarantee advertised HP numbers). But that is playing it safe, anyway, since their turbo cars almost universally put out more HP than claimed regardless of what’s in the tank.

  • avatar
    SCE to AUX

    Computer-controlled knock sensors pretty much eliminated the benefits of high octane fuel many years ago. Sure, it can provide slightly more horsepower at max throttle, but how often do you need that?

    • 0 avatar
      Scoutdude

      You’ve got that backwards, computer controlled timing using feedback from a knock sensor is what provided the benefit, not the computer controlling the knock sensor.

      Higher octane fuel does produce a benefit, if the vehicle is designed with it in mind. Use higher octane and you can run higher compression and more timing increasing the efficiency in all situations. The fact that the Caddy had such a big jump is the fact that the cyl deactivation means those cylinders that are working are doing so at a higher effective compression ratio and thus can extract more energy from the same amount of fuel if there isn’t a need to reduce timing.

      The thing is there are two ways to use a knock sensor. Traditionally when the computer sensed knock it pulled out a fixed amount of timing for a fixed interval. The other option is to use it the same way the computer uses the O2 sensor and that is to learn the current octane and provide an optimum curve based on what it learns. Ford and GM do that which is why they have a number of vehicles that say premium recommended vs required.

    • 0 avatar
      ACCvsBig10

      How, the computer still adjust timing based on detection. Begin able to run more timing on higher octane fuel can also give you better fuel econonmy when cruising and part throttle

      • 0 avatar
        toplessFC3Sman

        This is only true if the engine was designed with a higher compression ratio and/or greater reliance on boost that higher octane would allow, and only at high loads. At low loads (steady-state cruising, part throttle), most engines are not knock-limited, so higher octane fuel doesn’t do anything for them.

        A basic 9 or 10:1 compression ratio naturally aspirated engine (designed for 87 octane fuel) won’t see much difference, since the combustion is already optimally placed with low-octane fuel and more spark advance doesn’t get you anything (and could actually hurt economy, depending on how the engine controller responds and the trade-offs required by the fuel to go from 87 octane to 93 octane, such as the addition of more ethanol).

        However, an 11 – 12:1 compression ratio naturally aspirated engine, or a downsized, boosted engine that is designed for 93 octane will need to do one of two things (or possibly both):
        – Position the combustion event later in the expansion stroke (retard the spark) to avoid the higher P’s & T’s that will cause knock with low octane, which essentially gives away some of the piston’s ability to extract work during expansion, hurting efficiency & power.
        – Over-fuel the engine for the amount of air to get some charge-cooling benefit from the excess fuel, causing it to run rich and not extract the energy from all the fuel injected. Generally this will hurt efficiency a lot, but the power will be largely the same or slightly greater.

        However, if you are an OEM, by building an engine that requires (or recommends) higher octane fuel and gets a benefit from using it, that allows you to put this engine in bigger vehicles (or use a smaller engine than you otherwise would for the same vehicle), you get a benefit from the relatively smaller engine in both friction and pumping at low loads.

  • avatar
    thelaine

    Some vehicles need higher octane to prevent pre-detonation “knock” under hard acceleration, up steep hills, towing etc…

    I have such a vehicle. I don’t like paying for the higher-priced gasoline, but my 2004 (“hemi”) truck engine demands it in order to run properly.

    Hey Triple A, pre-detonation is bad, mmmm kay?

    • 0 avatar
      SCE to AUX

      Your 2004 truck isn’t fitted with a knock sensor? They’ve been used for 20-25 years, at least. A knock sensor retards the ignition timing when it hears the knock occurring, so quickly that you rarely hear it.

      • 0 avatar
        thelaine

        SCE, I am pretty confident it has a knock sensor, although you know a hell of a lot more about everything mechanical than I do. Nevertheless, I get that “dieseling” “valve chatter” sound whenever I drop the hammer with regular unleaded. It has been like that since it was new, and the engine is otherwise rock-solid and trouble-free over a decade later, so I don’t think it is a malfunction or the result of wear or build up of combustion products.

        The owner’s manual calls for mid-grade “preferred” but not required. So, I get about 12 or 13 miles to the gallon and use premium. Not economical, but still a great truck.

      • 0 avatar
        MBella

        Knock sensors are reactionary. It takes them a second to react, especially when engine loads shift quickly. When I used to work at a Mercedes dealer in the Seattle area, my test drive route had a hill that would always get a bit of preignition at the top of the customer fueled with regular. The knock sensors would quickly adjust, but I would prefer to avoid it all together.

      • 0 avatar
        raph

        Depends. Ford for example couldn’t work out using knock sensors in combination with a supercharger until 2010. The mechanical noise would interfere with the knock sensor.

        They also skipped on wide band 02 sensors until 2010 or 11.

    • 0 avatar
      OzCop

      Hmmm, what a difference 10 years can make…my 2014 1500 hemi does not require premium fuel. I have done the “treat it to a tank of premium” thing on relatively long trips, using Shell V fuel exclusively, with no noticeable difference in fuel economy or power. OTOH, my brother, a Chrysler Dodge tech for 48 years, swears by the premium stuff. In his opinion, and indeed his findings over the years, premium burns much cleaner in the cylinder, produces less carbon build up, and less valve train issues…

      That said, I purchased a new Ford Focus ST this year, and have an 05 SRT 4 Dodge in my garage. Both of those require premium as per sticker and owners manuals. But, of the 5 vehicles in my fleet, the other two being Fords, one an RV with a V10, and the other my wife’s Titanium Escape, with turbo, get only regular fuel…

    • 0 avatar
      Scoutdude

      Virtually no modern vehicle needs the higher octane to prevent knock, they have knock sensors to prevent that.

      However how they use those knock sensors does vary greatly from vehicle mfg to vehicle mfg and sometimes the vehicles with a mfg.

      You’ll note all of the vehicles tested are those that the mfg recommends the use of premium (for maximum power and economy) and do not require it.

      Those Ford and GM vehicles have adaptive timing tables so the vehicle learns the octane of the fuel currently in the tank. Others just have a default amount of timing they remove when a knock is sensed, and will return to the standard timing curve as soon as the knock is gone. thus the requirement for those.

    • 0 avatar
      Russycle

      When I had an XJ6, I ran regular in one tank and premium in the other. Usually ran off the regular tank, but on hills I’d switch to premium. Definitely climbed stronger on premium, could rev higher without knocking.

      • 0 avatar
        WheelMcCoy

        Shades of 007! I did not know Jaguar had 2 gas tanks. Pretty cool.

        • 0 avatar

          While I know this vehicle is outside of the conversation, my 84 Shelby Charger required premium, as per manual and sticker, so that’s what I ran. I would still get knock until I changed plugs from Champion to Bosch Platinum. Did not knock on the Bosch so I stayed with them for the life of the car. I assume better burn over the Champion plugs. Would that be the case?

  • avatar
    pwrwrench

    It would be interesting to run that test with something like this:
    https://vpracingfuels.com/product/c9/
    Gasoline has more energy, per unit weight, than ethanol. No one, in the more than 30 years that it has been a ‘thing’ here in California, has been able to explicate how oxygenating motor vehicle fuel will reduce exhaust emissions. It will work in a lawnmower, leafblower, or chainsaw, but in a modern computer controlled engine? (Giant eye roll).
    And don’t get me started on MTBE.

  • avatar
    tod stiles

    Don’t we talk about this once a year or so? Or am I just getting old?

    • 0 avatar
      SCE to AUX

      We do. And it seems to be studied every few years.

    • 0 avatar
      WheelMcCoy

      Yes, it’s tradition! This study happens to be the most thorough to date and is backed by real numbers. The AAA study is a little dry, but Engineering Explained on YouTube dives in with a very clear break down

    • 0 avatar
      ClutchCarGo

      Clearly at this point the multiple octane options at the pump are just a play on the buyer’s emotions. Just like how Starbucks will sell you a range of beverages with prices varying by 100% of the starting price, even though the beverages consist of materials and labor that vary only by 15% at most. How do feel today, worried about how your world is shaping up? Here’s your $2 cup of coffee. Or do you feel flush and positive? Here’s your $6 caramel macchiato deluxe. Same thing with gas. If it’s payday, go for the premium. If payday is still a week off, regular will do.

  • avatar
    slavuta

    Will AAA cover the warranty too?

    I had nice conversation with Lexus representative on this issue. They said officially – use recommended gasoline (premium). In the Renegade’s manual it says (for 1.4 multiair) “you can damage the engine if you don’t use recommended grade gasoline”. For their 2.4 version this statement was absent. But it also doesn’t have Premium as recommended for 2.4.

    I personally follow one of the simplest ways to deal with this issue – I only buy cars with 87 gas required.

  • avatar
    TMA1

    This Mustang GT information is relevant to my interests. I know Ford says 93 is recommended, but 87 is acceptable. I’ve recently switched to started putting in the midgrade stuff instead of 93. No issues so far, and still has more power than I can reasonably use.

    Midgrade costs 40 cents more than regular where I live, and premium is another 50 cents more than midgrade.

  • avatar
    alfaromeo

    The problem is CAFE. Using premium fuel is much easier to improve MPG than working hard on engineering drawing board. Manufactures have to meeting MPG requirement not reducing fuel cost.

  • avatar
    alfaromeo

    The problem is CAFE. Using premium fuel is much easier to improve MPG than working hard on engineering drawing board. Manufactures have to meet MPG requirement not reduce fuel cost.

  • avatar
    jack4x

    To me, the most interesting takeaway is that the much heavier Escalade ESV with the 6.2 had better fuel mileage than the Ecoboost F150 in every test condition, and using either octane fuel. I realize it’s a simulation, but 26+ mpg from a 420 hp, 6000 lb vehicle is impressive no matter what. I’ve driven plenty of 6 cylinder midsize cars that would struggle to maintain that economy, even at 65 mph cruise.

    • 0 avatar
      Russycle

      Yeah, that’s amazing mpg for 6+ liter V8. My 4-banger Scion barely does better.

    • 0 avatar
      focus-ed

      Sure. “Each vehicle was tested on a dynamometer.” So goes the 26+ mpg. It’s unlikely that any of these cinder-block shaped hulks of metal can achieve their EPA fuel economy at highway speeds. Maybe at high altitude (and going down). This is how the system is gamed. Add some city driving and mpgs will drop into teens. Oh well, gas is “cheap” now so who cares.

  • avatar
    Lorenzo

    My main concern isn’t the octane rating, but whether it’s a top tier detergent gasoline. That and regular oil&filter, air filter, and fuel filter changes will keep the engine and injectors in good shape.

    • 0 avatar
      saturnotaku

      ^ This. Nothing but Top Tier gas touches my tank. Costco is part of this, and it’s typically .30-.50 cheaper per gallon than Shell, et al. Even if you have to spend $60 for a membership, you can pretty easily make it back and then some on fuel alone, not to mention the other perks.

      • 0 avatar
        slavuta

        Same AAA had this research. But they also said, if you put non-TT gas and then TT gas, the second will clean up the stuff. Now, it worth saying that they used special engine.

        “This particular engine test has been an industry standard for more than 15 fifteen years because the orientation and temperature of the intake valves during the dynamometer test cycle accelerate intake valve deposit formation. This allows fuel marketers and vehicle manufacturers to screen different gasoline detergent additive packages in only 100 hours of testing.”

        Lets see. 100h in my daily routine means 3,600 miles. So, I can drive 3,600 miles till deposits start appearing. Then I going to put some TT gas and they will be washed away. This is beauty.

        https://www.aaa.com/AAA/common/AAR/files/Fuel-Quality-Full-Report.pdf

    • 0 avatar
      carguy67

      Fuel filter changes are overrated. I had a ’96 Ranger I fueled mostly at the corner independent (‘Rotten Robbie’) station (87 octane). When I sold the truck to my dad at 112K miles I cut the original fuel filter open out of curiosity (40K changes were recommended by Ford, IIRC). The only contaminants were a few tiny flecks of what appeared to be black plastic; as the truck’s tank was made out of black plastic I attributed these to crud left over from construction. My ’08 Mustang GT with 130K miles has never had a fuel filter change, and one of my Austin-Healeys has gone 130K miles with nothing but stock, thimble-sized wire screen ‘filters’ with no issues. It’s a profit center for service facilities; if your fuel supplier has gunk in their tanks fill up somewhere else (look for stations with lots of business; their fuel isn’t as likely to go stale in the tanks).

      Also, the RR station usually has 10 cent pricing gradients; i.e. midgrade (89) is ten cents a gallon more than regular (87), and ‘premium’ (91–I’m in California) is ten cents more than midgrade. For a buck or two per fill-up I’ll take the extra 5HP or so.

      • 0 avatar
        MBella

        The detergents aren’t for large particles that your fuel filter catches. They’re for fine particles that pass through your filter and form varnish on components.

      • 0 avatar
        krhodes1

        Many, if not most modern cars don’t even have replaceable fuel filters. It’s part of the pump, and when you get a new pump you get a new filter. Which will be sooner than later should you happen to get a tank of gas with a bunch of crud in it at some point. But that rarely happens, so I don’t particularly worry about it.

    • 0 avatar
      jfk-usaf

      Exactly (in reference to Top Tier post)… I’m less concerned about a mile per gallon or 2. I would also love to see a comparison and the resulting ratings of each brands detergent additive packages.

  • avatar
    volvo

    My comments on the article

    1. Here in California premium is usually $ 0.25/gallon more. That is about 8% higher cost. Numbers still favor regular.

    2. What gasoline was used for the test? California formulations gives my V6 RAV4 about 10% poorer fuel economy compared to my driving the same vehicle in the Northwest and Southwest states even though all fuels are 10% ethanol.

    3. Like Avgas the less premium drivers use the higher the price of premium will become. Sounds counter intuitive but refiners have no compelling reason to produce premium and refinery capacity limitations will determine the amount they produce vs regular.

    4. Unless you live in Iowa or Southern Illinois or work for Big Ag IMO there is no reason to support the ethanol mandate. Big Ag support and early Iowa primaries combine to tip the balance in favor of continuing the mandate.

  • avatar
    28-Cars-Later

    But, don’t many of these miracle 0.1L ICEs require premium?

    Funny that.

  • avatar
    toxicroach

    Allow me to settle the octane issue for everyone and for as long as ICE engines are a thing.

    Consult your owner manual. It will tell you what octane gas the engine wants. Use that octane.

    You’re all welcome.

  • avatar
    Alfisti

    Between my wife and i we only average about 20,000km a year but we both drive vehicles that state we must use premium fuel.

    It really bothers me as the price gap from 87 to 91 is a solid 25 to 30c per litre here which is just effing crazy.

    My question is not one of performance, it is one of reliability, any data on this?

  • avatar
    thelaine

    “4. Unless you live in Iowa or Southern Illinois or work for Big Ag IMO there is no reason to support the ethanol mandate. Big Ag support and early Iowa primaries combine to tip the balance in favor of continuing the mandate.”

    Truth. The ethanol mandate has always been pure graft, wrapped in bullsht, and sprayed with expensive perfume.

  • avatar
    olddavid

    I believe that deluding myself should be my own business – nobody else’s. What better reason to buy Ethyl?

  • avatar

    I’ve always felt (whether correct or no) that over the long term using lower octane fuel in a higher performance engine will result in buildup and perhaps premature wear.

    • 0 avatar
      George B

      I do maintenance on my girlfriend’s daughter’s hand me down 1998 Mercedes E320. Mercedes requires premium, but regular 87 octane gasoline has been used in that car from 150k to 250k miles with no noticeable problem. The engine leaks oil, but doesn’t smoke. It’s a rugged taxi cab with some unnecessarily complex luxury features added.

    • 0 avatar
      WheelMcCoy

      That would be difficult to test, but my unscientific side feels the same way. If a car can get better fuel economy *and* more power — usually contradictory demands — then make it so and buy premium. A happy engine is a clean engine.

  • avatar
    tomLU86

    30 year ago, if I recall, premium 91 was about 15%-20% more than regular 87; my 86 GTI had a knock sensor, premium was “recommended” and that’s what I used, so I paid $1.40 vs $1.20 typically

    Today, in Michigan, premium is an amazing 30% MORE! $2.35 for 87, $2.70 for 89, and $3.05 for 91. That’s a little rich for me.

    I’ve never used mid-grade. Either premium or regular.

    Now, unrelated to above, here’s my question: If I take a gallon of 91 and mix it with a gallon of 87, logically my octane would be 90. Is that correct?

    If I take 2 gallons of 87 and mix with 1 gallon of 93, my octane will be 89.

    So, instead of buying 89, I could save a little bit by buying 87 and mixing with 91. What do you all say to that?

    • 0 avatar
      WheelMcCoy

      Yes, this is my understanding, and your math is correct. It’s unbelievable how large the price gap has grown between 87 and 93. It’s 60 cents, give or take, in my area.

      • 0 avatar
        krhodes1

        Not unusual for it to be $1 in SW Florida. At which point my GTI and my Saab get regular – but I try to keep my foot out of it a bit more. Under $.50/gal, they get premium. Both are “runs on anything, premium recommended for highest performance”. And both makers are right – they perform better on premium. But not $1/gal better, even as little as I drive. <10K this year between both cars, including driving the Saab from Maine to FL, and an 1800 mi round trip escaping Hurricane Irma in the VW.

    • 0 avatar
      Steve65

      Your math on the first mix is wrong. If you mix one gallon of 87 with one gallon of 91; (87+91)/2= 89. Which is exactly what happens at the station. For a station offering 87, 89, and 91, there are only two underground tanks. One 91 and one 87. The dispenser mixes them 50/50 when you pump midgrade.

  • avatar
    dal20402

    Even if the knock sensor compensates quickly for knock by pulling timing, I’d rather avoid as much knock as possible altogether. So I run premium where required (my old Acura Legend) or recommended (my LS460). I don’t drive that much and think of the difference in price as part of my maintenance costs.

  • avatar
    stingray65

    My parents X3 with the 2 liter turbo (which “requires” premium) gets about 25-26 mpg at 70 mph highway speeds on regular and does 28-29 under the same conditions with mid-grade premium, so obviously the timing and or mixture is adjusted when it detects the good stuff. Perhaps the computers are not as sophisticated on most of the brands tested in this study, and hence only adjust to avoid knocks.

    • 0 avatar
      krhodes1

      In my experience, having owned a bunch of turbos – it makes way more difference in turbo engines than it does in non-turbos. With a turbo, the ECU can control timing and boost – usually backing off timing first, then boost. Less boost means you put your foot in it more at part throttle to get the same response, and it turns into a bit of a vicious circle.

  • avatar
    turf3

    I suspect very few people have run the experiment that I did, when I bought my Volvo S60 (turbo 5). It is the first modern car I have owned for which premium gas is recommended.

    I used premium for one full year, then used regular for one full year (thus eliminating seasonal effects). For my driving, a mix of city and highway, mostly driving moderately but occasionally stepping hard on it, I found zero difference in fuel economy. I never experienced any detonation that I could hear (knock sensor and timing control doing their jobs). I was not able to perceive any difference in performance; I do not delude myself that my butt will be able to distinguish a single digit percentage change in torque or horsepower at WOT, unlike some people who claim they can tell the difference between 250 and 255 HP.

    As far as I am concerned, for cars with a knock sensor and modern engine controls, the case is closed except for a few weird outliers that are probably out there.

    • 0 avatar
      random1

      I haven’t done a one year test like that. But I do an identical run every weekend from the NYC suburbs to Vermont. Exact same route and load every time. I’ve tried it with the “pure gas” I can get in Vermont (93 octane, no ethanol) down to regular old 87 (Costco and Mobil). I didn’t find any measurable difference in fuel economy or “seat-of-the-pants” power. This is in a ’00 E320 wagon, ’14 LR4, and ’14 V6 Touareg. Haven’t tried in the ’15 GTI (too small for the trip really), and never bothered trying premium in a ’12 Sienna.
      So really cannot justify the premium premium at all.

  • avatar

    Now show us what E85 will do in a turbocharged vehicle.

  • avatar
    Fred

    On my cars that require regular, running premium doesn’t do anything.
    On my old Elan, it pings like crazy on regular, even with premium a half a can of octane boost helps. Now on to modern cars

    1986 SVO, had a switch to cut off boost and retard the ignition if you put regular in it. On the 2007 Audi A3 with turbo 4 and a chip, I lost about 2 mpg and some power running regular. With a 2014 2.4 TSX wagon, I notice no milage change but the VTEC roar seems a bit muted.

    Your results will vary.

    • 0 avatar
      WheelMcCoy

      TSX Wagon here also. Using 87, I lose about 1-2 mpg in local driving. Mpg loss on the highway is negligible. Yes, VTEC seems to be muted with 87. Sticking with 91 or 93.

    • 0 avatar
      krhodes1

      I would not dare even attempting to run anything but premium in my breathed on Triumph Spitfire. It knocks to the point of needing octane booster on 91! Now that I can get 93 again in Maine it is a much happier camper. Of course knock sensor? Yeah, right, this car doesn’t even have vacuum advance on the distributor!

      Saab invented APC back in the early ’80s to allow running low octane gas on turbo motors. Knock sensor based boost control. But it reduced the fun factor considerably to do so. And Saab tuned the system such that the more octane you gave it the more go you got – there was nothing so fun as a tank of Shell 94 on a cold winter’s day in my ’85 900 Turbo.

  • avatar
    cimarron typeR

    I reviewed article, I would have liked for them to have monitored knock retard at ECU level,fuel trims etc. with 0BD2 scanning.
    I remember several years ago I experimented with our 2000 MDX switching between 87 and 91 octane for 2-3 tanks each. There was a 2-3 MPG swing positive with premium and a noticeably more responsive throttle response in the summer heat , so I just kept using 91.
    I’ll keep using premium in our cars that recommend it ,as they are turbocharged.

  • avatar
    brn

    This has been splattered across the news and I despise the headlines (not just TTAC).

    With most things, you reach a point of diminishing return. At some point, it doesn’t make economic sense. Same appears to be true for octane in gas.

    To me the real story is that the study proves higher octane DOES HELP. Does it make economic sense to get that extra few hp? That’s up to you.

  • avatar
    bubbajet

    I just can’t bring myself to buy a daily driver car that requires anything more than regular unleaded for “optimum” performance. If I raced, that’d be something else. If I raced, I’d run race gas (which I ran in my dirt bikes) to get the stupid ethanol out. I’m no automotive engineer, but it just seems…lazy on the part of the manufacturers.

    I’m in the market sometime in the next six months or so, and I’ve test-driven a bunch of cars. The Mini was a contender, until I found out it’s a premium fuel car. Shoot, it’s not that fast or smooth. The new Honda Accord with the 1.5T and a CVT was a far nicer engine/transmission experience on regular 87 octane. Oh, and the Accord gets far better mileage than even the tiny Mini with the small engine.

    Your mileage may vary.

  • avatar
    Add Lightness

    The way I see it is higher octanes do not explode as easily.
    If they don’t explode as easily, doesn’t that make them less efficient than a fuel that explodes more easily and quickly?
    Marketplace had an episode on this and the emissions jumped when a vehicle that requiring regular was fed premium.

    • 0 avatar
      White Shadow

      No, it’s all about the ignition timing. If the air/fuel mixture fires too soon, that’s where the problem lies. So to avoid that situation, a knock sensor will retard the timing once knock is detected, which also cuts engine power and economy.

  • avatar
    E85

    just use E-85. it’s around 100 octane, and way cleaner than any dirty petro-fuel.

    the best fuel would be E-95, with 5% water (hydrous ethanol, in other words), with high compression.

    run E-95 in a diesel, with a cetane enhancer, and you’ve solved all your problems.

  • avatar
    cbrworm

    This gets rehashed all the time, on all the forums. There are many cars that require premium – not just recommend it. High compression, non direct injection motors cannot pull enough timing to not knock destructively without seriously messing up emissions and power delivery while potentially damaging components. There are moderate compression engines that can have timing advanced to take advantage of higher octane, and also timing pulled for lower octane. If your car has a high compression engine and the owners manual says Premium only, you are risking significant physical damage to your engine by running lower octane gas with the engine under any significant load – even at low RPM. Maybe it will be fine if your driving conditions are correct, but jab the throttle at the wrong time and you risk instant damage before the knock sensors can react – they have to hear the ping before they can pull timing. If it is light pinging, no problem. If it is major pre-ignition, the damage can be done in milliseconds. You may not see the damage right away, pounded ring-lands, cracks in the edges of the piston crown, bearing damage from the impact. It may just show up as increased oil consumption and general noise, but it is cumulative and it is real.

    If Premium is recommended, it is your choice, the ECU will probably adjust. If the book says Premium Required (which 3 out of my 4 vehicles require), AAA is doing people a disservice by making it into a question of cost-effectiveness.

  • avatar
    Tele Vision

    My CTS-V requires premium so that’s what I feed it. The Ford truck and the Equinox don’t so they run regular gas. Weirdly, many people still think that premium fuel has more power per unit and will do stupid things like fill up with premium before a cold snap or a long road trip. Regular gas has more ‘bang’ than premium gas: octane being a ‘bang-inhibitor’ that allows for higher compression like that in my Cadillac. A lower-compression engine simply doesn’t require that much octane so using the more expensive gasoline – that results in a loss of power and poorer fuel economy – instantly puts you upside down in financial terms. Just this past Summer a friend was complaining about his Kawasaki Mule not running as well as it used to. It turns out that he’d filled it with premium fuel a few months earlier as, in his mind, some kind of a favour to it. The lack of performance was noticeable with three big guys in it.

  • avatar
    tankinbeans

    I think I read that each grade fuel tested for this comparison was E10 indicating 10 percent ethanol. Any fuel with ethanol is less energy dense than fuel without ethanol, if I understand the chemistry correctly. It follows that all things being equal if both grades have the same energy density, and the timing voodoo isn’t required, then on a strictly fuel economy/cost basis E10 87 is preferred.

    However, in my state certain brands off E0 91 at about $0.50 more than E10 87 (mid-grade has been bumper up to E15 88). On E10 87 my combined mileage in the 2017 Mazda6 – with 13:1 compression – is 28 (I don’t break it down city versus highway because I never have a tank that’s 100 percent one or the other), but with E0 91 my combined mileage is usually 33-35.

    I top up at half tank and have recorded each fill in fuelly with notes regarding grade.

    Am I understanding the chemistry correctly in that E10 is less energy dense than E0, or is there something else at play?

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