Why do many WEST states have MAX of 91 Octane?

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I noticed that many western states have maximum of 91 octane fuel whereupon the eastern states are 93 octane? Why is that?
I have a VOLVO Turbo XC60 so I am wondering if I should run a high octane fuel.
 
Elevation- lower air density means lower cylinder pressure, which means lower octane requirements.
 
Well, it's higher than STL.

Humidity? Does that play a role as well. Dry, less dense air?

Originally Posted By: tempnexus
Even in Phoenix AZ? I mean they are not that high above the sea level.
 
Originally Posted By: 440Magnum
Elevation- lower air density means lower cylinder pressure, which means lower octane requirements.


Yep.

Down here all gas stations have 93 octane.
 
In Denver (el. 5280 ft.) we had 85, 87, and 91 octane -- this in the late '90s. I was buying 91 for my 420SEL when a member of the local MB Club told me that even on the older cars without a knock sensor, the midgrade 87 worked fine. I tried it and had no power or other issues. When I set out to come back to NO, I made sure to fill up with the 91 before I dropped down out of Raton Pass and drove at lower elevations.
 
Originally Posted By: javacontour
Well, it's higher than STL.

Humidity? Does that play a role as well. Dry, less dense air?

Originally Posted By: tempnexus
Even in Phoenix AZ? I mean they are not that high above the sea level.


Hotter temperature is less dense...drier is more dense...so, Phoenix is less dense in summer...

They refine and market the fuel for higher altitudes...which is fine for a normally aspirated engine.

But my old Volvo Turbo Wagon, which I owned when I lived in Colorado, would develop the same manifold pressure in the Eisenhower tunnel as it would at sea level. So, the lower octane was not ideal for that car.

Now, my Volvo V70 T5 (HP turbo engine) is currently in Colorado. I have a boost gauge (aftermarket) on that car, too. I can't tell exactly how the engine management system handles absolute manifold pressure, but it seems to generate the same numbers at full boost/RPM that it did in Virginia Beach.

With the same manifold pressure, I would think that the detonation concern would be the same. Granted, the Bosch ME7 system is far better than the Bosch CI in my 1985, with a multitude of sensors, including knock sensor, so I worry less...

But I agree with the OP - I should be able to get 93 out there so that I can get the best engine performance.

As an aside, nothing was more fun that taking my shoe-box shaped Volvo 240 turbo wagon into the mountains. Its measly 165 BHP wasn't competitive with a lot of cars at sea level...but once you got to 10,000 feet, the normally aspirated Corvettes and Porsches (at the time) were making even less as they wheezed along in the thin air and I took great satisfaction in passing them on mountain roads...
 
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Originally Posted By: tempnexus
I noticed that many western states have maximum of 91 octane fuel whereupon the eastern states are 93 octane? Why is that?
I have a VOLVO Turbo XC60 so I am wondering if I should run a high octane fuel.


In California it's a state law that 91 is the maximum octane approved for sale for street vehicles.

It's part of the California-only reformulated gasoline regulations -- CaRFG3. Only specific blends are allowed to be sold. Always at a huge mark-up over other states (according to a recent report, $0.73/gallon!), and hugely profitable for the few formulating refineries that keep supplies tight.

You can buy other fuels only at stations serving off-road vehicles, such as at race tracks and marinas.
 
I've seen 85.5 while driving through Montana.

I've wondered why MFGers don't state that when driving at increased elevations they can use a lower grade. Maybe they're afraid of some kind of malfunction?
 
Probably too confusing.

Can you imagine the owners manual that says if you are in X,Y or Z you can use 85, but if you are P, D or Q you must use at least 87...

They just make the worst case scenario as the recommendation and move on to more parts of the manual 99.44% of the population will not read.

Originally Posted By: RamFan
I've seen 85.5 while driving through Montana.

I've wondered why MFGers don't state that when driving at increased elevations they can use a lower grade. Maybe they're afraid of some kind of malfunction?
 
Originally Posted By: javacontour
Humidity? Does that play a role as well. Dry, less dense air?


To my understanding, the lack of humidity by itself actually raises the required octane a little bit. I guess humidity has a stabilization effect on the air charge...so more water vapor in the air means less oxygen for spontaneous combustion, and a lower octane requirement. Super dry air, compared with humid air of the same density, has more oxygen and more potential to combust, raising the octane requirement.
 
The real reason is a bit simpler. Too many executives in CA driving cars that need premium gas. That's why most cars that say it needs premium have 91 as a minimum octane. On the east coast you can mix some 93 with 87 to get 91. No such luck on the west coast. There's lots of car in CA where it's basically close to sea level, same as the east coast. You can only get so much premium of a barrel of oil so if they sell more premium, they have to lower the octane. Emissions is a nice theory, but a lot of east coast states have adopted CA emissions. I think there's about 14 states that have adopted CA emissions, many of them on the east coast.
 
Originally Posted By: Wolf359
The real reason is a bit simpler. Too many executives in CA driving cars that need premium gas. That's why most cars that say it needs premium have 91 as a minimum octane. On the east coast you can mix some 93 with 87 to get 91. No such luck on the west coast. There's lots of car in CA where it's basically close to sea level, same as the east coast. You can only get so much premium of a barrel of oil so if they sell more premium, they have to lower the octane. Emissions is a nice theory, but a lot of east coast states have adopted CA emissions. I think there's about 14 states that have adopted CA emissions, many of them on the east coast.


Nice try, I think this theory isn't correct because you can crack and crank to the blend you want.
 
Originally Posted By: PandaBear
Originally Posted By: Wolf359
The real reason is a bit simpler. Too many executives in CA driving cars that need premium gas. That's why most cars that say it needs premium have 91 as a minimum octane. On the east coast you can mix some 93 with 87 to get 91. No such luck on the west coast. There's lots of car in CA where it's basically close to sea level, same as the east coast. You can only get so much premium of a barrel of oil so if they sell more premium, they have to lower the octane. Emissions is a nice theory, but a lot of east coast states have adopted CA emissions. I think there's about 14 states that have adopted CA emissions, many of them on the east coast.


Nice try, I think this theory isn't correct because you can crack and crank to the blend you want.


It's basically a supply and demand theory. It's been mentioned before. Makes a lot more sense than anything else posted earlier. And while it's true you can crack to a spec, you can only do so much and even if you could, the cost would be higher. Maybe the cost of gas is high enough on the west coast that it's not worth going that high? I'm told you can get 100 octane in CA, but it's not a big seller due to the cost.
 
Originally Posted By: Astro14
. . . As an aside, nothing was more fun that taking my shoe-box shaped Volvo 240 turbo wagon into the mountains. Its measly 165 BHP wasn't competitive with a lot of cars at sea level...but once you got to 10,000 feet, the normally aspirated Corvettes and Porsches (at the time) were making even less as they wheezed along in the thin air and I took great satisfaction in passing them on mountain roads...

Yes -- my 185 hp MB 280CE (the gas engine coupe, the Euro-market model) and the 201 hp 420SEL both handled the mountains with ease, and the big V-8 in the 420SEL got better fuel mileage at 5K feet than it did at (below) sea level here.
 
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