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Discussion Starter · #1 ·
So I was looking at Overkill's web site and they ask you to select 87 or 91 octane..............2010 3500 Impala

What do most of you run? 87 or 91

What happens if I buy a 91 octane computer and run 87 octane gas?

Which is going to give better mileage

I'm buying one for sure which one ?


Huggs Shannon
 

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When you contact them you tell him what you want to use. If you want to use 87 tell him that and that you want your tune for fuel mileage based on that octane.

He's pretty flexible.
 

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Keep the 87, unless your gonna put on a power adder IE blower or turbo. There is no reason for a 91-93 octane tune.
 

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Makes your VISION, stop & stare
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when getting my tune i asked will the same statement. WILL stated if i get the 87 octane i can run 91 fuel on the tune. but if i get 91 tuned octane than i cannot run anything lower than 91. at that time gas was around $4.15 a gallon for 87 oct so i just got the 87 tune knowing that 91 was alot expensive.
 

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You really should figure out the true cost of 91 vs 87 for the whole year based on how many miles per year that you drive. For example I drive 12,000 miles per year and the difference for me is only $12.50 per month (12,000 miles divided by 24 mpg = 500 gallons x $.30 more per gallon = $150 divided by 12 months = $12.50 per month! The problem is most people don't figure it out on a calculator, they just assume it will be huge bucks!
 

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Makes your VISION, stop & stare
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Yea but when you have power add ons, MPGs is way different bcus of a heavy foot. It all depends on the driver. See for me I knw I will never see or dream about 24 MPG. It just won't happen.
 

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Good Point 1impalavision1 but the fact is the formula works no matter what your average mpg is, and most people are surprised by how little money premium gas will cost them. I mean c'mon most of us are spending big bucks on our cars and/or other toys, fast food, alcohol, clothes, electronics etc. so even an extra $30 per month is really no big deal!
 

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Yea true but it depends if people can afford it at the time of needing gas. Some prefer cheap gas just to get them to point A and B. And some use premium to save there engine and actually care about there car.

I see food as a needed thing and premium gas is just a want.
 

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Yea true but it depends if people can afford it at the time of needing gas. Some prefer cheap gas just to get them to point A and B. And some use premium to save there engine and actually care about there car.

I see food as a needed thing and premium gas is just a want.
Also agree :eek:k3:
 

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I like least plus my car really seems to like cheveron gas the best an plus runs so much better like brakes tires loose with traction control on then computer detunes
With 12:5:1 does really need it I think does anyone really know any different
 

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I only use 87 octane in my 3.9L and it works just fine. I just got overkilled and now my car accelerates perfectly. The 87 octane tune is just what these cars need.
 

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There is a difference for the octane question. It would be for the timing advance rate and max total timing. With 91 octane he can adjust the amount of timing advance to take advantage of higher octane to make more power. If you say 91 , then try to run 87 IF he ignores the knock sensor you would get detonation (ping) if he sets the curve for 87 octane its a less aggressive curve rate. You could run any octane on this without issue. If he doesn't ignore the knock sensor , then the ECM should retard the timing until the pining stops. Some of the old muscle cars ran 12.5:1 factory CR. Maximum with pump 93 octane is around 10.5:1 CR with aluminum heads drop a point for cast iron.
 

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I usually run 91 octane in my 2013 LTZ not because of more power but here in central NY 91 octane is ethanol free and that is just plain good for our cars especially DI motors like the 3.6. Every GM tech I've talked to said our cars are meant to run on 87 but if you find ethanol free they go for it. I've also seen a gain is MPG with it. Probably because it doesn't have ethanol in it to gum everything up.
 

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What about flex-fuel Impalas - I'm assuming that since they are designed to run ethanol (up to 85%), that 10% ethanol isn't going to hurt anything, right?
 

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I found out from a dealership that the flexfuel car changes many different parameters in the computer to run E85 and if you want to switch back to regular gasoline you have to take it in and have the computer retuned. That 10% can hurt a flexfuel because it tuned to burn regular gasoline and that 10% gums up everything. When your car is running E85 it has totally different burn cycle. My car is not flexfuel and I was running 93 octane for awhile then I switched to 91 octane 3 full tanks in it is a totally different car. I can only imagine what it will run like when I have the upper intake and valvles cleaned.
 

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Saywhat? At least a few folks here switch between E85 and regular gasoline without having to take it back to the dealer to get re-programmed! Surely, the computer will automatically re-adjust the parameters when switching between the two? The owners manual certainly doesn't support that statement either. I don't buy that one at all....
 
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