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Old 05-28-2016, 07:44 PM   #11
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We have only found lower octane gasoline available where the surrounding terrain is over 2000' above sea level. In years past a vehicle with a carburetor performed ok on a lower octane. That is not true with today's vehicles and fuel injection.

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Old 05-28-2016, 08:09 PM   #12
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That's seems odd. You would want higher octane in thunder air to maintain power. With generators they recommend premium.

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Old 05-28-2016, 08:27 PM   #13
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I believe it because at higher altitude you have less air. With a NA engine you would get less air in and the compression ratio would drop. The exact opposite that happens with boosted engines. Also my generator calls for premium gas because it does not have alcohol, not for more power.

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Old 05-28-2016, 08:57 PM   #14
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17Racer, I have done that. 85/86 octane for regular is standard in the US rocky mountain states.

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Old 05-28-2016, 10:22 PM   #15
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Used to use nothing but 85 octane when I drove gasoline powered cars with no problems. I live at 6600 feet ASL. When I owned Ecoboost powered trucks, I used premium 91 octane because the high altitude didn't affect the turbocharged engine and premium gave better performance-timing was not retarded with lower octane.

High compression 2 stroke sled engines get premium/high octane fuel even at our altitude. UTVs get mid or premium grade despite fact that they run at 10k ASL...they run hot and high octane helps prevent detonation at higher temps.

Most cars do just fine on 85 octane at high altitude.
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Old 05-29-2016, 06:19 PM   #16
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Originally Posted by john mcneely View Post
Some areas do not have 87%. When confronted with this would I be better off with 86% or 88%?
Since owner's manual specifically says 87, I go with the higher. I know others cheat and use the lower for better price, but I care about the engine on resale, not that it would make that much difference....
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Old 05-30-2016, 02:55 PM   #17
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Gas engines without turbochargers run just fine and safely on lower octane gasoline found at higher altitudes. The air is thinner and the combustion pressure is lower so the engines don't need the higher octane. The lower combustion pressure is why they develop less horsepower at higher altitudes. The engine works like you never fully open the throttle. Also, modern engines have knock sensors that simply dial back the power if you happen to get below normal fuel, so your engine is still protected.

My advice: If you have less than 87 octane gasoline at higher altitudes, don't worry about it. If you happen to see lower octane gasoline, below say 5000 feet altitude, don't buy it.
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Old 05-31-2016, 11:36 AM   #18
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Originally Posted by 17Racer View Post
What would happen if you put 20 gallon of 86 octane and 20 gallon of 88 octane?

You would have 40 gal of 87

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Old 05-31-2016, 12:06 PM   #19
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If your vehicle calls for 87 octane, at higher altitude states like CO, UT, WY, ID, etc, regular gas will be 85/86 octane and will work just fine.

HOWEVER, if you are turbo charged, then yes, you will need 87 octane, regardless of altitude.

When traveling through high altitude states like CO, WY, UT, etc, I plan my fuel so I don't end up with a tank full of 85 octane when I hit lower altitudes.

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