85 Octane
Thread Starter
JK Enthusiast
Joined: Jan 2007
Posts: 271
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From: Utah
I am sure you are right in that there is power loss for alittude, but the 10% seems high.
I think I am going to run 87 for a while and then switch to 85 and see if I notice anything.
JK Jedi Master
Joined: Mar 2007
Posts: 14,800
Likes: 374
From: Midwest City, OK
Not to be pedantic (okay, I am being pedantic), but I'm not sure what "lower levels of oxygen" means. Technically (from a layman): 85 octane is usable because of the lower pressure of the atmosphere (the percentage of oxygen in relationship to the other gases should be essentially the same for elevations at which humans drive Jeeps). Octane designates the susceptibility of gasoline to premature detonation from pressure and heat rather than from the spark. The higher the octane, the less chance of premature detonation. The lower the pressure of delivered air, the less chance of detonation. High compression engines (rarely seen these days) and turbocharging/supercharging, which both increase cylinder pressure, also increase the need for higher octane fuel. Conversely, running at higher elevations reduces the need for higher octane. Thus, you see 85 octane fuel at gas stations at higher elevations.
JK Super Freak
Joined: Dec 2007
Posts: 1,750
Likes: 1
From: WV relocated 2 Dyess AFB, TX
Not to be pedantic (okay, I am being pedantic), but I'm not sure what "lower levels of oxygen" means. Technically (from a layman): 85 octane is usable because of the lower pressure of the atmosphere (the percentage of oxygen in relationship to the other gases should be essentially the same for elevations at which humans drive Jeeps). Octane designates the susceptibility of gasoline to premature detonation from pressure and heat rather than from the spark. The higher the octane, the less chance of premature detonation. The lower the pressure of delivered air, the less chance of detonation. High compression engines (rarely seen these days) and turbocharging/supercharging, which both increase cylinder pressure, also increase the need for higher octane fuel. Conversely, running at higher elevations reduces the need for higher octane. Thus, you see 85 octane fuel at gas stations at higher elevations.
Experience here. I lived in Colorado Springs ( 6,035 FT ) and ran 85 octane in all my vehicles (2005 Toyota Tundra and 2006 Hyundai Sonata). Both recommend 87octane and have a similar compression ratio to our minivan engine. Run the 85 octane. There is no benifit to running higher octane fuel. Premium grade is a marketing ploy to get you to spend more money; as said before higher octane is for forced induction and high compression engines.