mpg with 91 vs 87, in your prius c

In unscientific way I see about 2mpg (or 4%) improvement, and gas in our area as wjtracy mentioned is 10% alcohol across the board. Since alcohol is not produced locally and has to be trucked for compliance only we do not get alcohol contamination, both grades are 9%. At last pump stop the difference in price was 19c $2.239 for regular vs @2.429 for premium, or 8.5%. So technically penalty for using premium is 4.5%, or ~$.80 per tank.

Once again in unscientific way car seems to have less vibration and more power at light throttle openings. Perhaps due to more advance timing? You'd expect that on high compression engine with knock sensor ECU can advance ignition more with higher octane gas.

Now with better LRR tires and lower speeds car would spend more time at light throttle, so it is conceivable that the improvements for some hypermiler could exceed 4%.

I am curious if replacing "C"'s pretty restrictive air filter/box could improve MPG.

To OP are you running car with ECO mode on or off?

 

the reason for recommending premium is the compression ratio of the internal combustion engine. unless very late designs such asmazdas any CR over 9: 1 needs 91 octane to avoid retarding spark advance (avoiding knock) which reduces mpg. funny on a car so touted as wonderfully green at near $50k vs $30k for prius equivalent. Ah, the wonders of marketing.
shelf has nothing to do with it. both 87 and 91 octane will degrade in about 3 months. tha'ts why you should add fuel stabilizer in your lawn mowers left unused for 3 months.

 

the energy in either 87 or 91 octane varies enough that your mpg will vary as well. yes, it is possible to get more mpg from a tank of 87 than 91 for that reason though not often. the mixture of chemicals that make up gasoline varies considerably based on the source of crude. and the processing conditions necessary at the refinery to yield the needed amount of gasoline - and other products.
ECU's will advance spark advance until knock is not sensed, Don't know about your area but gasoline here is delivered from storage fields with ethanol already diluting the gasoline. the higher the ethanol content the lesser your mpg as ethanol has much less energy per pound than gasoline mixtures. and the extra cost for 91 octane is about 33% over 87 octane, we are lucky here because we get BP silver for 20% penalty. worth every penny. and on a prius the advance that is useable is not great enough to yield much better mpg.
at light throttle there little effort required of the engine so vibration is less likely.
hypermilers here regularly get over 100 mpg in contests but then a bicycle rider runs over them.

 

Oh I love a good fuel discussion. But basically, I wouldn't waste any $$$ on 91 or 93. There are some scenarios where 89 could be beneficial (uphill, 5 passengers, on a 120 degree day with the A/C on in high altitude). But aside from extreme cases, 87 is actually more explosive than 91...thereby producing more combustion energy. But as others have said, E0 93 will be more explosive than E10 87, so, in that case it would be beneficial to MPG to run the 93. But yeah, stick with the 87 guys, and run mid-grade under extreme conditions to prevent possible detonation. =)

 

How fast do you think cyclists move, on average? A reasonably fit rider might average 25 mph on a flat surface for a short distance.

These guys averaged close to 30 mph over 1300+ miles and got 110 mpg.
Team Achieves 110 MPG Average In Prius : TreeHugger

 

Are you certain octane numbers are significantly correlated to the combustion energy? I am not saying they don't, but, from what I remember, octane numbers just quantify the ability of a given gasoline grade to tolerate compression without spontaneous ignition ("knocking")

 

That depends, but 16-20mph avg over 50-200mi distance is very reasonable for a reasonably fit rider.
In congested urban environment bicycles are usually faster than cars due to gridlock.

 

Yes. 87 is more volatile, more explosive. The knock (detonation) is caused because combustion temps are too high and combustion is happening too fast. Higher octane fuel (lower combustion energy) however can make more power provided internal engine changes are made to accomodate those changes (higher compression via piston changes, cam lift and timing, advancing ignition timing...or in a turbo motor, more boost and additional fuel to compensate). I run e85 in my Subaru WRX and it makes 100hp more than my gasoline tune with the same parts even though it has far less explosive energy. As a result, injector size has to be doubled to flow more fuel, and a larger fuel pump installed. But, it also combusts at more than 200 degrees celsius lower and allows you to advance the ignition timing thus making lots more power. That cooling effect inside the cylinder allows for massive amounts of turbo boost (essentially increased compression) which would blow the motor on 91 in a heartbeat. While my 91 octane tune is limited to 19 psi no matter how many awesome parts I can put on my car...the sky is the limit with e85 and often other parts are the limiting factor. I currently run 23.5 lbs of boost and make double the factory Hp/tq to the wheels. E85 is 106 octane btw. =)

 

My oranges still taste better to me than your apples.

 

You are correct...I assume EconoModder is sort of saying the same thing...a lower octane fuel is more prone to autoignition...igniting by itself in contact with the hot surfaces inside the pistons before the intended time to ignite (which is when the spark goes off). In that sense we might call it it more explosive and/or more volatile but I would think "more prone to autoignite" the usual way to describe a lower octane rating fuel

 

Before or after you stuff them into your C tank?

 

In perpetuity, while you pull another non sequitur from your bag.

 

As the ancient saying goes, "For each incantation by prophet Uforya there be a wisecrack from one of the brethren".

Which makes the liturgy of High Empigism all the more soul-touching.

 

NONSENSE

 

I have tried both too and didn't measure any difference.

 

The next generation toyota Prius engine will most likely be direct injected which will run just fine on 87 octane even with 10% Ethanol. I have used a couple of tanks of 87 octane with 10% Ethanol in our 2014 volt with no ill effects. MPG varied on gas from 35 mpg climbing the Coast Range Hwy 26 passes and 42-44 mpg on the level highway. GM requires 91 octane or above for the Volt but it is good to know that you can use regular gas in a pinch.

 

Just for reference C does have knock sensor. Last time on gas station Premium was 38 cent more than regular. We got about 1-2 MPG better on premium in the past but this was not enough to cover costs.

 

I live in a hot climate and also see better mpg with 91 thus far with multiple tanks alternating from 87 to 91

 

Ha-ha-ha! LA is hot???

Back to topic: haven't tried Premium lately, with summer blend it is +0.38$, not worth it. I suspect bad 87 may be the main reason you are getting this difference. 5 years ago I took my motorcycle to California, and it didn't wanna run on CA gas at all.