Octane Needs at Higher Altitude

[mgood]

In different areas of the country, different octane ratings are sold as Regular Unleaded, Unleaded Plus, and Super Unleaded.
What they sell in a given area is, I believe, determined by altitude.

As you go up in altitude, the air is less dense.
Less dense air makes your engine less likely to knock, meaning you don't need quite as high an octane rating as you would at lower elevations.

Out of curiosity, I drove by three different gas stations this morning and wrote down the octanes they were selling as Regular Unleaded, Unleaded Plus, and Super Unleaded.
At an Alon we had 87, 88, and 90.
At a Phillips 66 it was 86, 88, 91.
Another Phillips 66 had 86, 88, 90.

Delray Beach, Florida, home of DiabloSport, is 9 feet above sea level, according to Wikipedia.
Denver City, Texas, where I live, is 3573 feet above sea level, according to Wiki.

The tuning programs are for 93 octane, 91 octane, and 87 octane gas.
For trucks, you just have the 91 and 87 as options.
I'm guessing that in Delray Beach, Florida, mid-grade "Unleaded Plus" is 91 octane and the "Super Unleaded" is 93. Am I right?
And the 87 octane tune is set a bit low for whatever crappy fuel you can find.

Right before I bought my inTune, I was about out of gas. I filled up with Super Unleaded because I'd read a little about the doo-dad I was about to purchase and wanted to try the super-whammy performance tune. (I don't remember the exact octane I bought in Lubbock, Texas, Elev. 3256', but it was probably about 91.)

Where I'm going with this, is that I suspect the tune written for 91 octane gas in Florida will work with mid-grade "Unleaded Plus" wherever you happen to be in this country. Around here that would be 88-89 octane.
If you're using the 93 octane tune, you use "Super Unleaded" wherever you are. I would have to go to an airport or racetrack to find 93+ octane fuel within 100 miles of here.

I've seen people on this forum say that if you use the high-octane tune with lower octane gas it will knock terribly and destroy your engine. I was under the impression that pretty much all modern vehicles had knock sensors and would retard the ignition timing if excessive knocking was detected. Or is there something in the tuning program that prevents that?
Thinking that even if I'm off on my reasoning and I use fuel of a lower grade than what's needed for a given tune, the computer should de-tune to protect the engine from damage. Am I wrong?

Help me out here. I am looking for input on this. I am no programmer, not a mechanic, and have very limited understanding of the physics and chemistry of this topic.

Also, anyone and everyone, feel free to post where you live and/or the altitude along with what octane ratings are typically seen at your neighborhood gas pumps.

[Mike_Levy]

Florida, and most of the East coast has 87, 89, and 93. Regardless of where you are, you should run the highest octane you can find, either 91, 92 or 93. I don't know WTH Alon gas is, but its certainly not one of the recommended ones, nor is Phillips. Funny how the state with tons of oil has the worst gas. DiabloSport recommends Exxon, Mobil, BP and Sunoco. I have stock in XOM, but BP is all my cars ever get.

[mgood]

I don't know WTH Alon gas is. . . .

Used to be Fina.

[13Cyclone]

For reference, typically above 3k Ft elevation, you can run lower octane. I'd research as much as I could for your particular vehicle but I've read in multiple places, racing forums too, that you can run a 93 tune on 91 octane around those elevations on up. Less cylinder pressure up high = less heat produced in combustion so it would be less prone to detonation. That said, do what you feel comfortable with so look around for more information.

[mgood]

That said, do what you feel comfortable with so look around for more information.

Thank you.
Asking questions here is part of my search for more info. Appreciate your input.

I haven't done anything yet. Still running premium gas. But right now I'm driving 123 miles each way to work. Gas has become a big part of my budget until I can get moved.

[jwdemon]

Down here in San Antonio we're around 700 ft. above sea level and I've seen 87, 89, 91 and 93 octane depending on the station. In some instances I've seen 89 at one station and 91 at another of the same brand with 87 and 93 as the other 2 available octanes. If you're more concerned with performance you should stick with the highest octane fuel you can get and the 91 octane tune but with that kind of distance to get to work I'd be more concerned with my pocket book and I'd use the 87 octane tune with the least expensive good fuel I could find.

[mgood]

. . . with that kind of distance to get to work I'd be more concerned with my pocket book and I'd use the 87 octane tune with the least expensive good fuel I could find.

That's kind of where I'm stuck right now. I put the 91 octane Diablo tune on my truck temporarily, just to try it. Never had any intention of keeping it like that. I intended to switch to the 87 octane tune pretty quick. But now that I have the Diablo tune, I like it and don't want to take it off. Started wondering if 91 octane is mid-grade in Florida and if I could run it on mid-grade gas here. Premium is expensive. With regular unleaded, I was putting $60+ a day into the tank. (OK, I don't make the trip every day, but several times a week anyway. This week and maybe next, I've got it made because we're working a big job 15 miles from my house. Everyone else is staying in a motel while I get to stay at home. )

[13Cyclone]

If you are over 3k feet, I'd try 2 octane numbers lower and datalog it looking for knock retard events.

[mgood]

If you are over 3k feet, I'd try 2 octane numbers lower and datalog it looking for knock retard events.

That's the plan. Just starting to look at how to log. Thought about doing it last night, but it was late when I realized I could do that.

Just starting to learn what this thing can do. My first tuner.