Real Gasoline, not Ethanol

If you are referring to the "or better" part, then that is because higher RON ratings (than for what the engine is designed) will not hurt the engine (and probably will not do anything of advantage either), but lower RON rating (than for what the engine is designed) may hurt the engine. A lot of modern engines can de-tune the engine on-the-fly to prevent knocking (and therefore damage), but in doing so reduces performance.

I conducted testing on my Prius, as I could not find any consensus when researching this point, and found my Prius ran without any apparent problems on all grades available in NZ – RON 91 (AKI 87), RON 95 (AKI 90-91) and RON 98 (AKI 93–94). However, RON 91 produced significantly less km per tank, in the region of 200 km less, when compared to RON 95. Also, performance felt sluggish on RON 91, especially under acceleration. RON 98 was +/- 50 km difference from the RON 95 tanks and performance didn't feel any different. Comparing price per km from my results showed that RON 95 gave me the the lowest price per km, even though the pump price is higher than RON 91. The price differential between RON 98 and RON 95 (being that RON 98 is higher again) makes RON 98 uneconomical due to no real increase of distance per tank. In all cases L/100 km (or MPG) results were consistent with the distance differences on each fuel.

As pointed out already, USA uses AKI (Anti-Knock Index – (RON+MON)/2) so you need to be careful when assessing different jurisdictions that you consider the correct units and compare apple with apples. Typically, AKI number is 4-5 less that the equivalent RON number.

As far as detergent packages go in our neck of the woods, minimums are mandated by law and as with a lot of corporates, they seldom go above and beyond what they are legally required to do. In their marketing, they typically try to imply that their top RON rated fuel is superior in quality and/or they imply the detergent package is better, but personally I think it is all a gimmick and stick to RON 95 regardless from which service station I'm getting my fuel.

My 2¢ worth.

 

Yes the EPA's gasoline recipe rules are probably out-dated now, cars are infinitely cleaner now.
There is some push for revising to a new 95 Octane formula.
However, you can bet your bottom dollar Ethanol Lobby will be fiercely demanding lot's of ethanol included in that new gasoline formula mandate, so there is no joy in Mudville if you like E0.

 

To be honest, I don't use E10 because I'm not really that concerned about the cleaner burning, the emission controls built into the car take care of any exhaust emission. To me it is the $8.50 per tank difference between E10 and U95 for the Prius and $23 for a full tank in the Ford. This means by using E10 I get the 5th tank full for free compared to using U95. I did try using no ethanol standard fuel but I though I was going to need to get out and push up the big hill out of Adelaide South Australia. the computer kept making timing and fuel adjustments in an attempt to stop the "pinking" and we steadily got slower and slower and had to battle for a spot in the truck lane :lol: Once it got over the hills it seemed to be ok, but it sure didn't like rapid take off or hill starts, so I carefully shop around to find E10 now rather than pay the excess for U95 or U98. The prius nor the Falcon return any better fuel economy on the more expensive fuel.
The VW Kombi runs best on LPG anyway so I avoid needing to add petrol as much as possible for both cost and performance. I did try U98 once and it really was a matter of throwing money away, it went no better and still used petrol like I had shares in an oil company.

T1 Terry

 

Yeah, Costco dropped E10 price to $2.45 per gallon now, 29% lower than E0 at my station! Altho other gas distributors have been caught, adding 10+% ethanol in their E10 gasolline, so their end-of-year sales, will help meet their yearly mandated sales of ethanol, there is no evidence that Costco does such things. Saying that tho, my year end tanks of E10 gasoline never set MPG highs, even when compared to general sub-average winter tallies of E10.

 

I was referring to the high octane fuel in what appears to be a low compression engine part.

I’d been under the impression the Prius was 13:1 but seems that’s not the case. I guess I should read up a bit on Atkinson cycle engines.

 

Here is the Wikipedia article Atkinson cycle - Wikipedia

Here is Toyota propaganda, good graphics, wimpy explanation:

As a shade tree mechanic, pumping Fuel/Air back into the intake manifold negates much of the point of a 'shorty' intake as they try to introduce cooler air, but the Atkinson cycle is going to 'puke' out hot F/A back into the intake manifold. Worse, if it is short enough you are pushing F/A back to the atmosphere, altering the ratio. (and throwing a code)
Since the goal of the Atkinson Cycle is to reduce the exhaust pressure to atmospheric, huge exhausts are not useful.

If there was room under the hood, forced induction would 'improve' the Atkinson cycle.

 

True on both counts, ta.

 

I think part of the gain made by pushing air/fuel back into the manifold is the improvement in chamber filling of the next cyl in the cycle that has its intake valve open. Very little chance of the air/fuel mix being pushed back out through the intake because the airflow below the butterfly is at a lower pressure than the airflow above the butterfly. Basically, what is ejected from one cyl will be pushed into the next cyl with its intake valve open because that is the area of the least resistance compared to reversing the direction of airflow through the butterfly.
The theoretical full cyl to combustion chamber ratio might be 13:1, but the cyl never actually fills each cycle because either the intake valve stays open and lets some back out, or the intake is so restrictive the cyl can never fill to capacity in the time frame the intake valve stays open. Forced induction would change that, but what would be the gain? The electric motors attached to the final drive can add 50+ kW from a standing start, why not better utilise that rather than trying to burn more fuel?

T1 Terry

 

At this station?
This GasBuddy item is timestamped several hours older than your post:

I currently see no area postings lower than this, though a Wal-Mart and a Valero on the south side are matching it.

 

Too bad the refineries up north are too far away fer ya. Told ya they were in a mini gas war.

 

Your location is marked as Everett, but Gasbuddy's Seattle zone extends beyond Everett up to Marysville, and doesn't show anything resembling that price. All the Costcos in this area are showing $2.69.

Looking at a map, the southernmost $2.45 I see is in Burlington, Costco and some competitors matching it or within a couple cents.

 

Thanks for reminding me, its time for a drive in the country. Well, well, well..... Burlington is along my route. Shall I gas up at the stations selling gas for $1 per gallon more than Burlington Costco? I don't think so.

 

For those living in IOWA, there are now 322 ethanol-free(E0) stations in the state, listed at pure-gas.org
I believe they had less than 100(?) say, 6-10 years ago? IOWA even passed my Washington state for E0 sources. Yea, anyone that unsuccessfully looked for local E0 in the past, may find EO closer to you now.