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Octane conversion based on Altitude

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Old 05-21-2011, 11:25 AM
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Kensai Kensai is offline
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Default Octane conversion based on Altitude

Okay, question for those that are very knowledgable about octane ratings.

Let's say, I am currently using 93 octane in low altitude areas like DFW. I drive up to Denver where the alttitude is very high. What would the premium octane equilivient be? I don't want to reprogram my RT back to 87 which is considerd mid grade in Denver. Denver's regular octane is 85. Their premium is 89 octane.

Can I run with 89 octane as premium fuel while driving in very high altitudes?

Dunno how the PCM would interpret the lower octane fuel even if it knows it is now in high altitude.
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Old 05-21-2011, 04:45 PM
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If you are using a 93 octane tune on you tuner and want to leave it with that tune then you only need the top grade fuel which at around 3000 elevation changes to 91 octane.

93 octane at sea level is the same fuel at lets say 3500 ft but only registers at 91 octane.
90 octane at sea level is the same fuel at lets say 3500 ft but only registers at 87 octane.
87 octane at sea level is the same fuel at lets say 3500 ft but only registers at 85 octane.


High grade "Premium" fuel is 91 here at 4500 ft.
Midgrade "Med" fuel is 87 octane here at 4500 ft.
low grade "Low" fuel is 85 octane here at 4500 ft.

If you are looking at grades on line, well some people call the best fuel Premium or Super, so it could be terminology issue. The numbers change because of altitude, not because the fuel is different and Denver has all 3 types so don't worry. In reality it's all about Government laws and Regulations that have to have a standard, that standard is at sea level, so the numbers are bigger but atmosphere psi's up here is lower then down there and that changes the number.


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Old 05-23-2011, 11:28 AM
Compactc9 Compactc9 is offline
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Out here in Denver our premium is 91, mid is 87, and regular is 85.
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