1. Attachments are working again! Check out this thread for more details and to report any other bugs.

mpg with 91 vs 87, in your prius c

Discussion in 'Prius c Fuel Economy' started by xraydoug, Mar 18, 2014.

  1. jhinsc

    jhinsc Senior Member

    Joined:
    Nov 25, 2010
    1,167
    259
    0
    Location:
    South Carolina
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    My v loves the temps from 60-70 degrees with partial grill block. Even though not quite accurate, the mpg indicator shows over 52 mpg on my new tank driving as I normally do. Likely won't last for long as temps climb above 72, I have to start using a/c when on the main roads where I don't want to roll down the windows.
     
  2. SageBrush

    SageBrush Senior Member

    Joined:
    Jun 4, 2008
    11,627
    2,530
    8
    Location:
    Southwest Colorado
    Vehicle:
    2012 Prius v wagon
    Model:
    Two
    If the vagon's meter is the same as the Gen3 Prius, it is about 5% optimistic over time.

    In balmy weather I average about 60 mpg in our Prius vagon when highways are avoided. Highway driving is about 50 mpg. Both values from the car gauge.
     
  3. xraydoug

    xraydoug Active Member

    Joined:
    Sep 14, 2013
    571
    176
    0
    Location:
    Roseburg, Oregon
    Vehicle:
    2013 Prius c
    Model:
    Two
    just an update of my results 87 vs 91 e10 in my prius c. I run my tank until the blinking light comes on and then I fill the next day or two.

    tank in feb. 87 e10 gave 52.9 calculated at pump
    tank in mar 91 e10 gave 59.6 calculated at pump (11% increase)
    tank in april 87 e10 gave 57.1 calculated at pump (4% decrease)

    now I have 91 e10 and the mpg so far is about 65, I think that as temps increase the mpg will also increase and that is why the increased mpg for my 2nd tank was large and my decrease in mpg for the 3rd was smaller at 4%. I think I will get 10% better compairing with my 3rd tank.
     
    orenji likes this.
  4. JimboPalmer

    JimboPalmer Tsar of all the Rushers

    Joined:
    Apr 14, 2009
    12,470
    6,862
    2
    Location:
    Greenwood MS USA
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    Actually it is possible that the meter IS the same, but the final drive ratio is different, as are the tires. My lifetime MPG according to the MFD is 41.8 while Fuelly. com is 40.2 Not bad.
     
  5. mahout

    mahout Active Member

    Joined:
    Nov 29, 2010
    655
    116
    0
    Location:
    NC
    Vehicle:
    2012 Prius c
    Model:
    Two
    As I explained many times the recipe for gasolines change with the crude received and the mixtures from refinery processing. The btu per pound of fuel is depent on the recipe. Its not difficult for 91 octane to have noticeably more Btu per pound and thus higher mpg. The problem is that 91 octane often has no ethanol so automatically that will result in a 6% increase in mpg due to the loss in combustion energy of ethanol. There are other compounds like tokluene increase octane AND the heat of combustion as well so increase mpg. Its an old trick used by racers to buy toluene from suppliers and enrich the horsepower for faster lap times in showroom stock races.
    Many gas distributors don't add ethanol to 91 octane because its more trouble than worth especially when hot rodders complain - bitterly.
    To really define the results onf using 91 vs 87 octane gas you'll have to check at least 10 tanks of each and also test for ethanol by checking the density of the gasolines. You'll have have a 'cup' that you can fill precisely to the same level and weigh each sample carefully. Yes, its tedious but more often than not thats science at work.
    good luck.
    BTW we did do that trial and except for the ethanol content we didn't find more than casual diffeences in mpg. The Fit current engine doesn't have the specs like increased compression ratio that can benefit from some 91 octane just like many supercars. The new Honda engine has followed Mazda "skyactive' in raising C.R. to increase hp and mpg. The only thing that concerns me is they have apparently reduced the drive gear ratio so there may not be much gain in acceleration but mpg appears to be the first spec that matters.
    cheers. and enjoy.
     
  6. SageBrush

    SageBrush Senior Member

    Joined:
    Jun 4, 2008
    11,627
    2,530
    8
    Location:
    Southwest Colorado
    Vehicle:
    2012 Prius v wagon
    Model:
    Two
    About 3.3% less energy in E10 compared to E0. Said in reverse, E0 has ~ 3.45% more energy than E10.
     
  7. xraydoug

    xraydoug Active Member

    Joined:
    Sep 14, 2013
    571
    176
    0
    Location:
    Roseburg, Oregon
    Vehicle:
    2013 Prius c
    Model:
    Two
    all street gas in oregon has e10, so I think I can rule out e0 on the premimum. im not sure it will take 10 tanks of each. I guess I would agree if I only put say 100 miles on a tank. anyway the second tank of 91 octane is giving much higher mpg again. just like the first one did. the engine warms up faster and goes to ev and I think that is part of how I am getting a boost in mpg. My driving is usually in town. I made a trip up the interstate last weekend and it dropped my mpg bigtime. just like with 87 octane, so I think the benifit of 91 may be better at low speed in town driving.
     
  8. xraydoug

    xraydoug Active Member

    Joined:
    Sep 14, 2013
    571
    176
    0
    Location:
    Roseburg, Oregon
    Vehicle:
    2013 Prius c
    Model:
    Two
  9. Emcguy

    Emcguy Member

    Joined:
    Sep 20, 2013
    176
    29
    0
    Location:
    Australia
    Vehicle:
    2012 Prius v wagon
    Model:
    N/A
    In AUS we have the entry level 91 RON (equivalent to USA's 87) and the E10 is 95 RON. In our 2012 prius v and 2012 yaris we measure no difference in mileage. I think that, even though the chlorific value of the E10 is 3% less, our gages need an extra decimal place more than the tenths of L/100km provided to see any change.

    Oh yeah, also the cost of E10 95 RON is $0.04 / L less than 91 RON $1.50 / L. I feel it's cost equivalent but helps the environment. ;-)
     
  10. tgpii

    tgpii Member

    Joined:
    Sep 8, 2012
    382
    63
    13
    Location:
    Tapier Lake/Orland Park, Ilinois
    Vehicle:
    2012 Prius c
    Model:
    Two
    Has anyone tried the 100 octane racing gasoline?
     
  11. xraydoug

    xraydoug Active Member

    Joined:
    Sep 14, 2013
    571
    176
    0
    Location:
    Roseburg, Oregon
    Vehicle:
    2013 Prius c
    Model:
    Two
    it is likely most people will tell you there is no benifit and you may damage your engine. I would be intrested to find out. my brother in law races but I think the fuel is higher in octane than 100 and he mixes with pump gas to make it less expensive to race.:)
     
  12. orenji

    orenji Senior Member

    Joined:
    Aug 17, 2013
    5,884
    3,486
    0
    Vehicle:
    2010 Prius
    Model:
    Three
    [quote="SageBrush, post: 1981349, member: 4155 This question has been asked and answered so many times, I feel like it is 1947.

    Once again: 91 Octane will not improve fuel economy in a car in which 87 Octane is recommended.[/quote]


    Where does it say that 87 Octane is recommended? 87 is the min. recommended octane.
     
  13. mahout

    mahout Active Member

    Joined:
    Nov 29, 2010
    655
    116
    0
    Location:
    NC
    Vehicle:
    2012 Prius c
    Model:
    Two
    As long as you use gas that is rated for highway use you're OK. I aleways refill at the gas pumps at the track with high test highway stuff intended for showroom stock racers that has no ethanol and I get 5-10% better mpg going home than coming to the track. No ethanol and better recipe naturally has higher combustion energy. Yes it adds 3-4 mph down the straights too.
    Do not use strictly racing gas as it may have some components that are not compatible with street legal carbs and fuel injectors; and of course it may not but I don't want to find out.
     
  14. xraydoug

    xraydoug Active Member

    Joined:
    Sep 14, 2013
    571
    176
    0
    Location:
    Roseburg, Oregon
    Vehicle:
    2013 Prius c
    Model:
    Two
    20140708_160329.jpg update on mpg
    tank in feb. 87 e10 gave 52.9 calculated at pump
    tank in mar 91 e10 gave 59.6 calculated at pump (11% increase)
    tank in april 87 e10 gave 57.1 calculated at pump (4% decrease)
    tank in may 92 e10 gave 67.7 calculated at pump (15% increase
    tank in june 87 e10 gave 57.81 calculated at pump(15% decrease) I forgot to log this when I filled up it is on fuelly.

    I currently have 350 miles on a tank of 92 e10 trying to make the 700 mile club. The display shows 74.1 mpg I need to get it up to 80 to be comfortable with 700 miles but I am going to try to make it comfortable or not:cool:

    This tank will not be good to evaluate the difference in mpg 87 e10 -vs- 92 e10. I think by now it is obivious that my car works much better on the 92 likely about 15% better.(y) the cost is much less that 15% more. I will likely keep going back and fourth for awile to try to be sure my results are likely to be the same for others who have lots of city driving a prius c in oregon.:)
     
    #34 xraydoug, Jul 8, 2014
    Last edited: Jul 8, 2014
    orenji likes this.
  15. Mr Incredible

    Mr Incredible Chance favors the prepared mind.

    Joined:
    Jun 23, 2008
    955
    506
    0
    Location:
    Neb
    Vehicle:
    2012 Prius c
    Model:
    Four
    From the owner's manual... One could make a case that it doesn't actually recommend 87 octane, but the bulk of people looking at it would get that out of it.


    Fuel types


    Unleaded gasoline (Octane rating 87 [Research Octane Number 91] or higher)


    Use of ethanol blended gasoline in a gasoline engine

    Make sure that the ethanol blended gasoline to be used has a suitable Research Octane Number as outlined n “Fuel types”.

    Use only gasoline containing a maximum of 10% ethanol. DO NOT use any flex-fuel or gasoline that could contain more than 10% ethanol, including from any pump labeled E15, E30, E50, E85 (which are only some examples of fuel containing more than 10% ethanol).


    I’ve tried 87 and 91, with NO ethanol, a number of times. There was absolutely zero difference in mpgs.

    I suppose the supremely anal and controled driver might be able to bring in some relevant numbers, but for the other 99.9999% of us I don’t think you could tell a difference greater than normal variability. Anything greater than 1% would be suspect, IMO.

    I couldn’t tell you what the difference there would be between the two with ethanol blended in, but I would think the blender’s art would be suspect as well. MAX 10%...doesn’t mean ALWAYS 10%. It also doesn’t mean they started with the same bulk gasoline every time. Too many unseen variables to call it good for everybody/everywhere. I think people are seeing a difference that isn't due to the gasolines.

    Just my $.02.
     
  16. orenji

    orenji Senior Member

    Joined:
    Aug 17, 2013
    5,884
    3,486
    0
    Vehicle:
    2010 Prius
    Model:
    Three
    So why does the book say "or higher"? Why not say 91 or higher is not needed, but can be used.
     
  17. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,474
    38,106
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    ^ In case the lower octane is not available, the station's run out or something like that?

    As far as I know, the only criteria for the higher octane is the need to resist ignition more, to avoid pre-ignition in a high compression engine (Corvette, Ferrari, etc).
     
  18. Mr Incredible

    Mr Incredible Chance favors the prepared mind.

    Joined:
    Jun 23, 2008
    955
    506
    0
    Location:
    Neb
    Vehicle:
    2012 Prius c
    Model:
    Four
    My Z28 owner's manual recommends 91, but it can use 87. I actually DO get better mileage out of 91 with it due to engine design.

    I can't always get 87 without ethanol. I refuse to use ethanol so have to buy 91. The C runs fine with 91, but doesn't run better. The mpgs are exactly the same. It is repeatable.

    Many cars can use 91 octane without issues, but it is not required to run properly. Using the proper octane can be a money saver if you don't have to use 91.
     
  19. wjtracy

    wjtracy Senior Member

    Joined:
    Sep 19, 2006
    11,309
    3,586
    1
    Location:
    Northern VA (NoVA)
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Since Oregon does not require reformulated gasoline, it is definitely possible your 91 octane is higher energy content. Those of us stuck with EPA RFG gasoline should not expect to see this advantage. So you do have some potential advantage on the 800 mile club. 15% exceeds my expectations but 8% or so is reasonable.

    If it was me I'd be taking an extra gallon sample to measure weight and calculate density, but that's just me. It's not definitely more energy rather it's just a possibility.
     
    #39 wjtracy, Jul 9, 2014
    Last edited: Jul 9, 2014
    ztanos likes this.
  20. xraydoug

    xraydoug Active Member

    Joined:
    Sep 14, 2013
    571
    176
    0
    Location:
    Roseburg, Oregon
    Vehicle:
    2013 Prius c
    Model:
    Two
    460 miles showing 76.7 mpg:)
     
    SageBrush likes this.