Yes, but that only matters at full-throttle, when there's no way to cram more air into the cylinders. In normal driving conditions at part-throttle, the driver or the cruise control will open the throttle more to compensate for the thinner air, and airflow and cylinder pressures will end up being the same as if the engine was at low altitude.
86 Octane in the western states?
- Thread starter BobsArmory
- Start date
85 octane in southern Idaho, 87 is mid grade there.
Absolutely. The mass air sensor only controls delivery of fuel and it will compensate for air density, but the tendency for knock to happen is lessened at altitude by cylinder pressure reduction due to the thinner air. Reduced octane at altitude is still proper today for fuel injected or carbureted motors.
I wouldn’t even run that stuff in my lawnmower let alone either of my vehicles. 87 minimum for all 3, the truck recommends 89 so that’s what it gets and generally what the lawnmower gets as well since I’ll fill them both up at the same time.
can confirm.... Mom's whole family lives around Twin Falls.
when they've taken her Taurus (2009, NA 3.5) out there on vacation, Dad read through the manual, it says something along the line of no lower than 87 octane.
I questioned this, when they got back, because he said "it said not to use 85 octane gas", and i was sure he was confusing 85 octane with e-85....nope.
...it clearly states not to use any fuel with an octane rating below 87...
They have high compressionSome modern (even non-turbo) engines say to use at least 87 octane regardless of altitude
I would think any savings the fuel companies make with selling lower octane fuels would be offset by the additional complexity of having so many different grades of fuel?? Seems like making just 87/89/91+ is a better business profit model then 85/86/87/88/90/91+ where even logistics of shipping is made more difficult. They should not offer less than 87 because no vehicles allow less than that...and altitude is never mentioned in any owner's manual as an acceptable reason to use lower octane.
Wherever I've seen the 85 octane offered in high altitude areas, they never offered 91. Just 85 and 89. I haven't been back much since e-15 became a thing and I don't recall seeing how that's rated there.
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The newer stations like Casey's have 4 grades of fuel around me and the alcohol is mixed at the pump. E10 87, E15 88, E10 91 and E10 93.
No additional complexity. Gasoline is blended of various refinery outputs with various octane ratings. Generally, the lower octane components are cheaper to produce. To make 86 instead of 87, you just vary the proportions at the refinery.
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