Project Farm testing impacts of octane and ethanol content on power and mpgs...interesting!

[MSCH]

Did you understand what I wrote and what others have noted? Yes it can be related to the octane rating if the engine can take advantage of being able to advance the ignition timing. Compression ratio is directly related to efficiency. The air/fuel ratio isn’t relevant here since it’s about extracting the most energy possible from the existing mixture. It’s not unmeasurable, you can watch the timing advance yourself if you’re so inclined.

But on the other hand there are a myriad of factors that influence fuel economy. As you mentioned the energy density of the fuel is also important. It’s one of the reasons why no one can accurately prognosticate about one specific variable, I once linked an article that showed that even at the same gas station the energy density varied about 4% and this was irrespective of winter/summer blends or other gross variables. Proper fuel economy testing in a laboratory always starts with standardized test fuel.

I tried to, but if you can't make your point in one or two sentences, well, you lost me. LOL.

 

[OVERKILL]

If acceleration is important to you, stick with premium fuel. Otherwise, regular will give you the best economy for going from point A to point B. From my records, I get no perceptible loss in gas mileage by using regular fuel where premium is recommended. All my cars have knock sensors.

I'll bet that 99.9999% of the drivers on the road, couldn't tell which octane of gas was put in their vehicles, if someone else filled it up, and didn't tell them.
My most driven car is a Honda Accord.
I use regular in it...but lets say that I lent it to someone, and it got really low on gas, so they stopped and filled it up with premium, then returned it to me.
Unless they told me, I would never know that they used premium instead of regular.

In fact on this very car when it was about a year old, and had always been burning regularly gas, someone told me to use premium gas and reap the better mpg, running smoother, and performance gains. So I tried 3 tank fulls of premium in a row in my Accord. There was absolutely no perceptible difference in how it ran, performed, or mpg.
I went back to regular, and no change.
About 5 years ago while on a vacation trip in it with my wife, she filled up with premium at a gas station, i was inside taking a wizz.
That night she told me that she put in premium, and that is the only reason I knew. Had she not said anything, I would have never known. I told her to buy the cheap stuff, it doesn't make any difference so why use premium.

Totally depends on the application. My 6.4L requires 91 or higher, and it sounds like you threw a can of marbles under the hood with regular. I discovered this because I was sold regular when I paid for 91 at an Esso station I no longer frequent. It would rattle like crazy under load, it couldn't pull enough timing to make the knock go away.

So, there are applications where it makes a significant difference.

My wife's truck will run fine on 87, but makes more power on 89/91.