86 Octane in the western states?

[BobsArmory]

So last last week I had to do a road trip. Left central Michigan for Phoenix Thursday Friday then return back to Michigan right away on Sunday Monday, total 4,500 miles driven. While stopping for gas I noticed many of the gas stations sold 86 octane fuel once I got past say Texas. I thought 87 was the standard for the USA. Any one know why states out west sell 86?

BTW I was driving a 2023 Equinox average mpg was 32 worst was 23, best was 40 plus while driving thru Texas with a huge tail wind.

 

[k1xv]

Yes. Except in turbo or supercharged cars that adjust manifold pressure to sea level pressures, the octane requirement of a naturally aspirated engine goes down as absolute barometric pressure goes down. Higher altitudes out west mean that engines are running on thinner air.

So the oil companies get away with lower octane fuels than they sell at sea level locations.

 

[frankbee3]

I think the 86 octane gasoline is sold in high elevation areas? I wonder if turbocharged cars would be more susceptible to detonation as a result?

 

[Snagglefoot]

Phoenix is at 1,000 ft but it’s interesting to note I-10 reaches 5,000 ft near Tucson.

 

[c502cid]

Actually we still get 85 octane E-10 as regular here. Anytime I see 86 it's E-15 and it's cheaper than 85. 87 is our midgrade and 91 is Premium. Years back 89 was our Premium but that was largely before computer controls on vehicles.

 

[Rmay635703]

Actually we still get 85 octane E-10 as regular here. Anytime I see 86 it's E-15 and it's cheaper than 85. 87 is our midgrade and 91 is Premium. Years back 89 was our Premium but that was largely before computer controls on vehicles.

When in mile high areas it seems like a grab bag of what types of gas will be at the pump, one national chain sells the same octanes no matter what elevation the station is at.(usually best deal as they only sell 87+)
Other places just have 85/87 and nothing else. In remote areas I’ve encountered a burned out ancient looking gas station with new pumps (unmanned) and all you got was diesel or 85, 80 miles to next gas station situation.
I also see dead octane values like 90 octane out west.

Even though my car requires 88e15 or premium per the manual it’s naturally aspirated so I just run a mix of 85 and whatever higher grade comes up at the next station.

It’s always amazing how much more expensive 87 octane gas is out west as compared to here, even the 85 is typically a bit more expensive.

 

[slacktide_bitog]

Some modern (even non-turbo) engines say to use at least 87 octane regardless of altitude

 

[eljefino]

E10 85 is like 82 octane base fuel plus the ETOH. They must look high and low for this garbage.

It's the second biggest ripoff in the world, only behind the $12 foot long sandwich at subway.

 

[c502cid]

E10 85 is like 82 octane base fuel plus the ETOH. They must look high and low for this garbage.

It's the second biggest ripoff in the world, only behind the $12 foot long sandwich at subway.

My 2000 Blazer and 1998 Civic, both not exactly performance machines, run just fine on 85. Lots of cars can run on it.

 

[subyski]

Yes. Except in turbo or supercharged cars that adjust manifold pressure to sea level pressures, the octane requirement of a naturally aspirated engine goes down as absolute barometric pressure goes down. Higher altitudes out west mean that engines are running on thinner air.

So the oil companies get away with lower octane fuels than they sell at sea level locations.

Turbo or supercharged engines are still impacted by altitude. The boost gauge may read the same but the absolute pressure (boost + atmospheric) that the engine sees is lower at altitude. The computer may compensate a bit by increasing the boost but at the expense of running less efficient.

Some modern (even non-turbo) engines say to use at least 87 octane regardless of altitude

I have yet come across any modern manual that says 85 is minimum but there are millions of people that drive on 85 everyday.

This has been a stickler for years. The lower octane ratings out west/higher altitudes were introduced during the carbureted car era, which makes complete sense. This stays true with fuel injection vehicles running with lower compression ratios.

However, despite arguments to change the lower level octanes with modern higher compression engines (n/a and forced-induction), refineries complain that it would cost money and the added bureaucracy, nothing actually changes. To counter any changes, modern cars are able to compensate at the expense of best efficiency and power. Running a modern high compression n/a engine with 85 and driving normal, any real difference is likely unnoticeable. Even with more turbo-charged engines available in normal cars, my bet is a majority run 85 because they see "regular" and the cheapest, if they were originally tuned on sea level 87.

 

[ammolab]

Turbo or supercharged engines are still impacted by altitude. The boost gauge may read the same but the absolute pressure (boost + atmospheric) that the engine sees is lower at altitude. The computer may compensate a bit by increasing the boost but at the expense of running less efficient.


Running a modern high compression n/a engine with 85 and driving normal, any real difference is likely unnoticeable.

“Driving normal”? Do we always drive normal?.. My Chevy is normally aspirated and rated at 415 hp, but I live on high plaines above 6000 ft. I notice the considerable loss of horsepower here due to thinner air. When I visit coastal Texas my drive train and rear tires are screaming, “whoa Big Guy..take it easy there”!

 

[subyski]

“Driving normal”? Do we always drive normal?.. My Chevy is normally aspirated and rated at 415 hp, but I live on high plaines above 6000 ft. I notice the considerable loss of horsepower here due to thinner air. When I visit coastal Texas my drive train and rear tires are screaming, “whoa Big Guy..take it easy there”!

Driving normal as in puttering around to work, grocery store, starbucks, the things that the majority of people do. If your "normal" driving is going flat out stop light to stop light or letting loose on an open highway, I would say use the appropriate octane to maximize power and engine safety regardless of altitude.
Nothing is going to make up for high altitude. Generally speaking, you are only getting a maximum of 340 hp out of your engine at your altitude. Going to sea level is going to feel like bolting on a small turbo/supercharger. Anytime I go out east, even normal cars feel somewhat boosted.

 

[D1sc]

“Driving normal”? Do we always drive normal?.. My Chevy is normally aspirated and rated at 415 hp, but I live on high plaines above 6000 ft. I notice the considerable loss of horsepower here due to thinner air. When I visit coastal Texas my drive train and rear tires are screaming, “whoa Big Guy..take it easy there”!

I know a lot of people can’t afford it but all my vehicles have a methanol system that allows for variations in octane the fluid is either straight methanol or boost juice 50/50 I just make my windshield fluid stronger for the truck and Audi but straight methanol in the vette.Saves you counting on the PCM to adjust the timing. I was raised on a dairy farm (77-85) my ex mechanic dad would fill a large bug sprayer with methanol with a rotary valve on our A model JD so when plowing no knock.It was something I didn’t appreciate till much later.Mobil near me,so it isn’t hard to get.

 

[twX]

Altitude shouldn't affect the likelihood of knock on most modern cars. Ignition timing is based on mass airflow, or sometimes manifold pressure. The engine doesn't care if that airflow is due to higher throttle/boost at high altitude, or lower throttle/boost at low altitude.

On turbo cars, knock may even be worse due to poor intercooler performance in thinner air, if ignition timing is based on pre-turbo air temperature at the MAF sensor, as it is on many cars.

The use of lower octane fuels at altitude is probably a holdover from the days of carbureted engines, which run richer at altitude.

 

[D1sc]

Altitude shouldn't affect the likelihood of knock on most modern cars. Ignition timing is based on mass airflow, or sometimes manifold pressure. The engine doesn't care if that airflow is due to higher throttle/boost at high altitude, or lower throttle/boost at low altitude.

On turbo cars, knock may even be worse due to poor intercooler performance in thinner air, if ignition timing is based on pre-turbo air temperature at the MAF sensor, as it is on many cars.

The use of lower octane fuels at altitude is probably a holdover from the days of carbureted engines, which run richer at altitude.

Knock sensors are what I thought was the make or break part of this equation.Since I once had a perfectly good LS7 destroyed by the tuner desensitizing them or what I guessed turning them off in a dyno tune.Needless to say I now have darton sleeves.

 

[benjy]

interesting reading with various "Opinions"! as far as pricing TAX $$$ vary by state!! her in Pa. land of taxes newer Sheetz have 15% eath 88 oct a little cheeper but mpgs suffer as eath has less BTU's. it was a lot cheeper at first + selling well but as usual it did NOT LAST!! when gas got $$$ i sold my beloved classic 72 cutlass 16 mpg for a new 2001 jetta turbo 37 mpg!! + peppy!! people complain BUT dumping that unneeded TANK SUV or 4 dr 4 wd pickup unless REALLY needed is an EZE CURE + being retired it matters NO more!!

 

[sloinker]

In Wyoming, 85 87 91 are the three common grades. The 85 and 87 usually contain ethanol. The 91 usually doesn't but that is on a station by station basis. Modern electronics will do what it takes to run the 85 octane. I have driven cars that recommend 92 octane with 85 and they don't seem to care. No knock or rattle, probably diminished performance and fuel mileage. I couldn't really tell. 85 MPH for hundreds of miles in a straight line across Wyoming, Utah, Idaho, Montana....until you hit the 87 octane regular on the West coast states and Nevada.

 

[eljefino]

The use of lower octane fuels at altitude is probably a holdover from the days of carbureted engines, which run richer at altitude.

An engine is an air pump, and it acts like it has lower compression when you feed it thinner air.

 

[ripcord]

I've regularly purchased 85 octane gas when in Montana where it's often over 5000 feet elevation. Never noticed a difference there in any car except for my old 64 Fairlane which had reduced power. I'm pretty sure it was because the carb was already jetted on the rich side at sea level and was even richer a mile high.

 

[Rmay635703]

E10 85 is like 82 octane base fuel plus the ETOH. They must look high and low for this garbage.

It's the second biggest ripoff in the world, only behind the $12 foot long sandwich at subway.

Straight run gas is 75 octane without additives, making 82 octane probably costs the refinery a nickel.

Funny how they charge more for 85 stuff than 88 is here