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Old 10-08-2008, 01:03 PM   #19 (permalink)
Master EcoModder
Join Date: May 2008
Location: Briggsdale, Colorado
Posts: 296

Wildfire - '96 Ford Bronco XL
90 day: 14.88 mpg (US)

Blackford - '96 Ford Bronco XLT
90 day: 20.26 mpg (US)

Y2k - '00 Honda Insight
Gen-1 Insights
Team Honda
90 day: 73.98 mpg (US)

Redford V10 - '01 Ford F250 Lariat
90 day: 15.64 mpg (US)

FireFly - '00 Honda Insight DX
90 day: 69.43 mpg (US)

LittleRed - '00 Honda Insight
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Thanked 31 Times in 14 Posts
If you don't change the timing of your vehicle, I can see where some will say that increase in octane sees little results. BUT, if you were to use 91, then adjust timing to where it just stops pinging, then you should see enough of an increase in FE to justify the expense. I did the math and found that by doing just what I said, 91 octane is more than worth using for increased FE.

With 85 octane, I get 54 mpg (+5 deg timing). With 91 octane, I get 60 to 61 mpg (+10 deg timing). It costs me $.065 per mile in fuel with regular and $.060 per mile with premium. My break even mpg would be 57 mpg. Anything over 57 on premium makes premium fuel the least expensive.

Using regular 85 octane, it will cost me $142.19 per month in fuel over 2200 miles.
Using premium 91 octane, it will cost me $133.08 per month in fuel over 2200 miles.

87 octane puts the numbers about midway.

I can't make it any clearer.
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