The what fuel is right for your car thread got me thinking. It seems 93 is premium east of the river, and 91 is the common premium west of the river. You do see the occasional places that sell 93 or 110, but it's exceedingly rare. E85 is pretty common here.
In reality, 91 vs 93, there isn't much of a power difference. I was just curious if anyone knew how it came to be?
Good question on the 91/93 split, but I can try to find an answer.
We have discussed the differences, though: 91 vs. 93 | Are you giving up power?
Funny enough, a lot of the Kwik Trips and Costcos here in the midwest sell 92. Splitting the difference? I'm guessing this is just non-ethanol 91 with enough ethanol added to get the extra point.
Shell, Sinclair, and any of the BP stations that used to be Amocos are the most reliable sources for 93.
I tune my cars on 91, that way I know I won't be stuck somewhere needing higher octane and not being able to get it.
TX has plenty of 93. It's west of the MS. Most of the high plains and mountain states have lower octane gas because of elevation and thin air.
It's rare in the plains but corn juice is really common so it balances out I guess. Get 91 no ethanol and then top off with the corn juice.
Hopefully, we'll get better answers, but living in Colorado, I've been told it has something to do with the altitude?
Best pump gas around is 91 and best ethanol-free I've seen is lower than that, maybe 89 or 90? Our normal octane grades are 85 and 91, but I can't remember the middle grade since I don't use it.
From an older SAE study : "octane requirements (of the tested vehicles)...were reduced, on average, by 0.5 (R+M)/2 per 1000 ft increase in altitude."
I remember buying gas in wisconsin a few years back and seeing 85, 88, 89, 90, 92. Kinda blew my east coast mind. I bought 85 even though my owner's manual says min 87. The ol' 4.0 didn't care.
I find it interesting that it's supposedly related to elevation. Summit County and Kansas city get the same octane.
And wish this had been posted earlier in the day as I interviewed Zach from Sunoco this morning for the next Fuel Tips.
We did discuss some fuel history, though: Why 110 octane race fuel exists and why it’s still so popular.
Now to write it all up.
AnthonyGS (Forum Supporter) said:TX has plenty of 93. It's west of the MS. Most of the high plains and mountain states have lower octane gas because of elevation and thin air.
I just drove to Lubbock from AZ saw plenty of 93 when we stopped.
The high elevation = lower octane thing really needs to disappear at this point. It applies to naturally aspirated engines up to a point (although not as much with EFI, as the computer knows about the thinner air and doesn't run richer and may also run more timing). And it's irrelevant to anything turbocharged (especially if the system is targeting boost as absolute pressure rather than relative to atmospheric), as it'll still build similar boost (just coming in a little bit later potentially).
In Canada we get a 94 high octane option in some areas. One of my cars it tuned to that, which means when I take it down to the US where 91 is the usual option, I have to take it easy as more throttle = more boost= more knock = more spark retard. That engine uses 25 psi boost, mind you. Another of my cars has no boost, a stock compression ratio of 11.5 and gets along just fine on 91.
In reply to L5wolvesf :
It's been about five years since I last drove through AZ and NM. I do remember the northern and southern parts of both having different grades (that elevation thing again).
In reply to wspohn :
Sunoco stations here used to have 85, 87, 89, 92, and 94 octane.
The 94 smelled nice, like low key race gas.
I'd like the answer as well. Altitude is certainly the reason that here in Colorado that "regular" is 85 octane. I don't think that's a reasonable answer as to why 93 octane isn't available at all, though. The choices here are 85, 87, and 91. "E85" is regularly available (though, in Colorado it's almost never actually 85% ethanol), and I've also seen E15 sold at 88 octane. Ethanol-free is available in some places, and it's almost always 91.
Turbo cars clearly need 91 even at altitude, and also benefit from 93. The Focus RS could certainly make use of 93 if I could get it, but I can't. So it gets 91, unless I'm filling up at a pump that has E85 available, in which case I'll splash mix a gallon of E85 with the 91, hoping for 93ish E15.
The Miata runs great on 85, even with timing bumped to 14 BTDC from the stock 10 and running the extended reach plugs that bump compression a little.
The 2020 Tacoma will detonate a bit on 85, even at altitude, when towing. Makes sense given that it's sporting an 11.8 compression ratio--kind of amazing that it runs on 87 at sea level? I'd think that whatever tricks they do to make that work would still work at altitude with 85, but I don't like the detonation even if Toyata says "some detonation is okay". It doesn't do it at 87, at altitude or at sea level. I've also never seen a vehicle manual that says "85 octane is okay over X altitude", but if it is, seems like they should specify that.
I was told that 93 wasn't pasteurized. 
if you got that, you're probably at least 50.
In California there is about 50 different blends if gasoline with fantastic taxes. If we had 93 I would be spending $8 a gallon.
In reply to Berck :
I found some VP additive at Autozone for a bit over $20 that claimed to raise fuel octane by seven numbers.
So, I tried it in 92. And the car (the 16psi Volvo) responded to it like when I sampled some 100 octane a while back.
I used the full quart in ten gallons. I am sure that a small dose per tank would give a noticeable bump.
In reply to Pete. (l33t FS) :
Once I stopped the ambulance in a gas station out in Shennandoah Nebraska- real edge of the panhandle with some really Nebraskan-wierd stuff. I've never seen a station with:
- 7+ different forms of fuel.
- E10, E15 and E85 with specific warnings and pumps for all of them.
- Tractor Diesel.
- Road diesel.
- 110 Octane race gas.
And ONE pump for gas. It was JUST gasoline, 91 octane, no ethanol or alcohol. I've never seen a station quite like it, and that counts the one that was cash only at 60% the cost of everyone else. I even live in podunk corn country and I've never seen a pump just for red diesel at a station before.
Here in Manitoba, Husky used to sell 94 and that's what everyone with a tune would run. They discontinued it a couple years ago, so the best we get now is 91 with up to 10% ethanol.
In reply to Pete. (l33t FS) :
This stuff? I wonder what it is. "Madditive Octanium is not meant for vehicles equipped with O2 sensors or catalytic converters." That's enough to keep me from trying it in the Focus RS. Also, expensive. I'm pretty sure I can get to 93 a lot cheaper without risking the cats by using toluene. But I'm not willing to do that either:) Before I rebuilt my Honda CB350, it liked to detonate on 91 octane. (The massive layer of carbon on the pistons when I eventually took it apart explained it.) The auto parts store octane boosters were mostly just MTBE which didn't really do much other than turn my spark plugs red. Toluene worked great...
AnthonyGS (Forum Supporter) said:TX has plenty of 93. It's west of the MS. Most of the high plains and mountain states have lower octane gas because of elevation and thin air.
Came here to say this. Altitude. It's been a couple decades since I was in Denver, but I don't recall ever seeing anything over 89 or 90 octane. Even in lower altitude midwest areas, they don't have hills which has a surprisingly large effect in cruise throttle position.
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