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87 or 92 octane??
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Junior User
Joined: Dec 2009
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87 or 92 octane??
Do you notice any difference in MPG when running on different octanes? I also have a shop in town that sells 24% ethanol blend and when I put that in my suburban it got better mpg especially when towing. Anyone use ethanol blends?
Sit. Stay.
Joined: Oct 2001
Posts: 18,308
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From: Washington State
There are only really two reasons why you should get better mileage while using a gasoline with an octane rating above 87.
1. The engine is in a poor state of tune which causes knock with the 87 octane which pulls down timing or...
2. The fuel is not actually the advertised octane due to age.
Higher octane fuel does not have more energy or BTUs than lower octane fuel.
Using 24% ethanol fuel will damage fuel system components. 10% is the maximum that should be used safely.
1. The engine is in a poor state of tune which causes knock with the 87 octane which pulls down timing or...
2. The fuel is not actually the advertised octane due to age.
Higher octane fuel does not have more energy or BTUs than lower octane fuel.
Using 24% ethanol fuel will damage fuel system components. 10% is the maximum that should be used safely.
Senior User
Joined: Dec 2009
Posts: 118
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From: Murray KY
I have not tested the difference with the 1989 429 4v but the 1992 454 TBI (in a MH)will gain enough mileage (power) to make 91 Shell V Power the same cost as Shell 87. The power is nice in the hills. In the newer vehicles I can not see better mileage with higher octane. Not sure the logic that enables this with the 454. It may advance timing until a knock is detected.
Senior User
Joined: Sep 2007
Posts: 183
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From: Ryegate, VT
I had a 84 one ton dually dump with a plow, It didnt matter what it got for gas; mileage was horrible, lots of grunt though!
I found that running the mid grade fuel in my wifes hemi pwrd dog, it got just slightly better mileage. So I spend the extra 2 to 5 dollars per tank for the midgrade gas.
I found that running the mid grade fuel in my wifes hemi pwrd dog, it got just slightly better mileage. So I spend the extra 2 to 5 dollars per tank for the midgrade gas.
Sit. Stay.
Joined: Oct 2001
Posts: 18,308
Likes: 20
From: Washington State
Steve, my post wasn't a joke. 
Even current PCM tuning cannot increase timing due to fuel type (hence the need for a tuner) so surely a 1992 OBDI isn't going to be able to. That 454 runs better with higher octane due reason #1.
Cando, the advertised HP for your wife's HEMI is from using 89 octane. Makes sense you'd see a decrease in performance using a lower grade fuel.
Even current PCM tuning cannot increase timing due to fuel type (hence the need for a tuner) so surely a 1992 OBDI isn't going to be able to. That 454 runs better with higher octane due reason #1.
Cando, the advertised HP for your wife's HEMI is from using 89 octane. Makes sense you'd see a decrease in performance using a lower grade fuel.
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