Grand prix GTP 1999 S/Ced running off 87 octane mods - Page 5 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 11-16-2006, 03:45 PM   #41
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Quote:
Originally Posted by anotherbonneville
So does this mean if i run my car with 93 octain i can gain HP and Milage?
Unless you're SCed, higher octane is definitely a waste of money. My mileage actually goes down the higher the octane (the harder to burn, the less efficient). I still run mid-grade, but only because my favorite station has it at the same price as regular. And because the stubborn pert of my brain still believes the myth that it helps on my N/A engine...
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Old 11-16-2006, 04:19 PM   #42
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Quote:
Originally Posted by BillBoost37
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Originally Posted by vital49
Nope. You will gain nothing from it other than a lighter wallet which may make you go a tiny bit faster.
IIRC other members with L27 and L36'* have mentioned seeing slight mileage gains from higher octane fuel.

SingsCountry1967 comes to mind, totally stock
Yes I did state that. Unfortunately, I'll need to retract that statement about the N/A at this point in time and I apologize for that. The car I found that out on was not the Bonnie. I made the error of assuming it was the same with all cars. It was with my 92 Cadillac, which likely required the higher octane.

I'm conducting experiments right now... it will take me at least a month or so (one tank per week) before I can make conclusions. I'm trying to keep the variables the same which may be difficult if the weather turns nasty (i.e. longer idleing time) and if the gas mixture changes (I usually see a drop in mpg around October. I have NOT seen it yet this year).

So far:
89 (midgrade) DIC MPG: 25.5 Calculated MPG: 24.5
1st tank: 87 (low grade) DIC MPG: 25.5 Calculated MPF: 23.0 (???)
2nd tank: 87 - tbd
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Old 11-16-2006, 05:10 PM   #43
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Quote:
Originally Posted by anotherbonneville
So does this mean if i run my car with 93 octain i can gain HP and Milage?
Not unless your computer can realize the higher octane gas and will increase your timing to compensate for it. Your mileage may not decrease, but you won't gain HP.
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Old 11-16-2006, 09:06 PM   #44
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So what your saying is it does make a difference in a supercharged car but not on a car like mine?
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Old 11-16-2006, 09:22 PM   #45
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Yep! Supercharged cars NEED it to perform to their potential, you don't.
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Old 11-17-2006, 12:01 PM   #46
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Well since buying my car in August, I've been putting 87 in it because of the gas prices. Yes yes...I know ...So after reading this thread a couple days ago, I decided no more 87 for me. Yesterday I filled up with 93, and thats the way it'* going to be from now on. Granite, god only knows what kind of gas the previous owner put in the car but atleast I'm putting the right stuff in now.
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Old 11-17-2006, 12:27 PM   #47
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You should see better gas mileage. So you're not taking the hit to the purse you think you are.
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