Refilled with non-ethanol 91 octane ...

[IFMJohn]

The whole higher octane fuel for fuel economy debate depends completely on the engine. Large engines tend to get higher fuel economy but only by 1 mpg or so. As far as getting more power by running higher octane fuel is a myth. And as far as running it to clean your engine out, again is a myth. Running a higher octane fuel cam actually cause buildup. Higher octanes have a longer burn time and require a higher pressure to fully atomize. Running higher octane fuel than designed can actually cause the fuel to not atomize causing the fuel to not fully burn. This can cause buildup and premature failure of emission components.

Its the good ol' "Some is good so more must be better." Except in this case it's not necessarily true.

[JustPassinThru]

Originally Posted by sickpuppy1

I'd always been told that octane would not help mileage, unless what your running is too low for the engine requirements. IE: High performance engine require higher octane, low performance engine runs on lower octane, and running higher octane in a low performance engine does not help. Going ethanol free could help, yes, but arent all Shell fuels ethanol free?

Not anymore - by law.

In fact, in many states it's ILLEGAL to sell booze-free gas.

Higher octane doesn't increase fuel mileage when you increase beyond the design requirement. IOW, if you run low-octane gas in an engine designed for premium, the control module will retard the spark to prevent pinging; but if it's designed for 87 octane, running higher octane does nothing.

But removing the booze, increases the mileage. Because there's FAR less BTUs per unit of fuel in alcohol than there is in gasoline. Moreover, depending on the design of the ECUs, ethanol can mess up the feedback loop.

I haven't kept track; I avoid ethanol gas for other reasons. But I seem to get about 2-3 more miles per gallon with gas then with the odd rotgut tankful I've gotten.

[mirapatec]

I recently achieved 44.4 MPG on a tank of non-ethanol 87-octane gas. I was extremely happy. This is with an automatic transmission and city driving, by the way.

[albee213]

I once had a Dodge/Mitsubishi Cult 1980 something and it was a 4 popper, I used different grades of fuel in it while delivering pizza and kept tight records and found at that time it was breaking even running regular or premium becuase I was getting 1mpg more at every fill up and I felt it was worth it, I live in Seattle and there are nothing but hills here and the car was just happier going up them with with Prem. When ever I get a new car I start with low grade and then move up slowly to see the difference and not only look at mpg but how does the car feel when taking off from a light, going up a hill and listen to the idle, does it purr nice and even or is there a little stagger here and there.

Does anyone know the compression ratio for the Yaris, I keep reading its 10.5:1 and that would be in premium area for octane ratings. 8's are normaly low grade, 9's are mid and 10's are usually for high performance engines.

I just put a tank of mid-grade in my 07 Yaris and it feels a little smoother when I jump off a light and when passing on the freeway. I used regual and got 35 mpg, in a week or two I will see if there is a difference with mid-grade. One think I cant complain about is my last car was at the pump twice a sweek at $60, now looking at $40 every two weeks.

[IllusionX]

The 1nz engine is 10.5:1 compression. But does not need premium fuel.
Non-ethanol will increase mileage and overall peppiness of the car.

[Ben_]

In theory noon ethanol gas should give better fuel economy because it has more energy pet gallon. It takes about 300x more ethanol to produce the same energy as gasoline. This is assuming that 10% ethanol has does have that much ethanol

[why?]

ethanol technically will add power, because it makes the octane rating higher. In fact the Subaru community specifically tunes their cars for ethanol to get insane hp figures.

Non ethanol gas will get better gas mileage, but if coming from ethanol gas it will take a few tanks, because with ethanol comes water, and it takes a bit to get that out of the fuel system.

The compression has nothing to do with the type of fuel you need to use. Your numbers might have been great in the 80's but today the economy cars have higher compression ratios.

Oh, and I think my best gas mileage came on the crappiest gas in my region.

Octane really isn't about the temperature of the way it burns, because all gas burns at the same temp. It is about the consistency of when it burns. Higher octane gas is harder to ignite, but it will all ignite at the same time more often, whereas lower octane is easier to ignite, and might not quite all burn at the same time.

[albee213]

I have done some research on the Yaris 1.5 engine and it is a 10.5 to 1 compression ratio and in a normal circumstances that would require the use of high octane fuel.

Using modern technology they have found a way to inject fuel into the engine without causing early detonation by redesigning the head and fuel injection system.

Now after saying that, I am old school and to me 10.5 to 1 is a high compression ratio and to get what I think is the best performance out of this little rice cooker I only use mid or prem fuel, here on the West Coast its only .20 cents more per gallon for prem over regular. I was just in the South and did notice that the price difference between reg and pre was more like .60 cents, now that might make me change my mind as well.

[SirDigby]

this was interesting. looks like it died a year ago. Octane rating is the ability for a fuel to resist detonation under pressure. that's it. there are two different methods for testing this; the RON method and the MON method. then the results of the fuel tests are averaged. R+m/2. a modern ignition system will advance the timing to the point of knock or ping then retard slightly. that point depends on the fuel used. THE YARIS manual states use fuel with RON 91 rating.

[SirDigby]

ethanol-free fuel is awesome! my civic averaged 10% better fuel millage when E-free.
I just started to test my yaris at high altitude to see if the results are the same.

[ern-diz]

Originally Posted by SirDigby

this was interesting. looks like it died a year ago. Octane rating is the ability for a fuel to resist detonation under pressure. that's it. there are two different methods for testing this; the RON method and the MON method. then the results of the fuel tests are averaged. R+m/2. a modern ignition system will advance the timing to the point of knock or ping then retard slightly. that point depends on the fuel used. THE YARIS manual states use fuel with RON 91 rating.

RON 91 rating is 91 octane?

I've had dudes go at me on here, basically laughing at me for preferring 91 octane. I've since tried some tanks of 87 and can't say I notice a difference in any measure other than my wallet. Still feels like I'm doing the old girl a disservice every time I pump 87, though lol.

[mirapatec]

I am still achieving higher mileage using the non-ethanol fuel. Around here, it is referred to as "marine fuel" since boaters use it.