ORIGINAL: Furinox

I'm not sure why people say the gas mileage is going to increase because it really isn't. If anything it is going to stay the same or go down. If you compare your current fuel mileage using 87 octane to your post tune mileage using higher octane of course you will get sligtly better mpg because of the higher octane. What I think most of you really want to know when you ask if your mpg is going to go down or up is if it will end up costing you more at the pump after a tune and my answer is maybe. Some of you may disagree but pre-tune lets say you are getting 20mpg using 87octane at $2.50/gal. You have a 16 Gal tank so 16x20=320 miles per tank. The highest octane is usually a minimum of $0.20 more per gallon so considering a slight increase in fuel mileage could be 22mpg? Ok, so 22x16=352 miles per tank. so for a fill up from bone dry 87 octane is $40.00, fill up from bone dry with 93 is $43.20.

So...with 87 octane you are paying 40.00 bucks for a tank of gas and getting 320 miles.
With 93 octane you are paying 43.50 for 352 miles.

Thats an extra 32 miles for $3.50 more at the pump

with 87 octane $.125 cost per mile.

with 93 octane $.113 cost per mile.


If your gas station only charges $0.20 more for the highest octane, and you actually see at least 2 miles per gallon increase while using it then it is about .01 cents more economical to buy the higher grade fuel.

Don't jump for joy yet. Other factors are going to go into account once you tune your car. It is my understanding that a CAI brings more air than fuel into your engine and that is why you require the tune. The tune tells the computer to add more fuel to the motor to account for the extra air thus giving you the extra power. Let me say that one more time, the tune is telling the computer to use MORE fuel. The amount of fuel we are talking about though is very minute.

It is my opinion from knowing what I have stated in this post that with a CAI and Tuner your MPG is actually going to go down, but so little that you wont really notice it unless you keep your foot in it.

All in all the Tuner/CAI is a great thing to add to your car for power and that little extra oomph. The only thing that is going to drastically change your fuel economy is you.