mpg with 91 vs 87, in your prius c

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.

 

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.

 

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.

 

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.

 

About 3.3% less energy in E10 compared to E0. Said in reverse, E0 has ~ 3.45% more energy than E10.

 

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. ;-)

 

Has anyone tried the 100 octane racing gasoline?

 

[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.

 

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.

 

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.

 

So why does the book say "or higher"? Why not say 91 or higher is not needed, but can be used.

 

^ 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).

 

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.

 

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.