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Old 07-21-2009, 07:29 PM
JackandJanet JackandJanet is offline
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Join Date: Aug 2007
Location: Among javelinas and scorpions near Tucson, AZ
Vehicle: 2005 Ford F150
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Quote:
Originally Posted by 2004f1505.4x4 View Post
I'm looking at an edge and I run 90 octane. Could I run a 91 octance and be safe?
It depends on a couple of things.

First, is your gas graded by the (R + M)/2 method? If so, the answer is "yes", but you might want to retard your timing by -0.5 degrees. However, what's your altitude up there? IF you are somewhat above 3500 feet (or a bit more than 1000 meters), you can probably leave the timing alone. Gas octane is reduced for fuel sold at higher altitudes because the altitude improves the anti-knock properties (while robbing you of power).

But, if your gas is graded using the RON (Research Octane Number) method only, DO NOT use a 91 octane tune. You are filling with gas that is only slightly higher in octane than our 87 octane. Use an 87 octane tune.

- Jack
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