The AKI (anti-knock index -- also known as "octane rating") of the fuel is an average of two different methods of computing the fuel's ability to resist engine knock. Regular unleaded gas in the U.S. has an anti-knock index of 87, while mid-grade is usually 89, and premium typically is 91 - 93. The higher the number, the more anti-knock protection the fuel offers.

Premium fuel does not necessarily pack more energy content than does regular. Rather, it allows more aggressive engine designs and calibrations that can extract more power from each gallon of gasoline.

The higher AKI (anti knock index) of premium gasoline does not in itself make it any cleaner than regular gas. Oil companies, however, like to advertise that their premium fuels are ‘specially formulated” to clean fuel injectors, restore lost power, etc. But the truth of the matter is that any “cleaners” that are added to gasoline itself are not going to be present in sufficient quantities to do that much good. With the money you save by running the recommended octane of gasoline for your engine, you can afford to put a bottle of quality fuel injector in the tank once in a while to help optimize fuel injector spray pattern.

The key word here is a “quality” fuel injector cleaner, like BG44K, Chevron Techron to name two of the proven players. Stay away from the el-cheapo fuel injector cleaners that you see lining the shelves of the parts stores. They really don’t work all that well.

How much will you save by running regular? That depends but for an average driver, you can save up to $200 a year, maybe more. Gasoline retailers and refiners like to sell high-test premium fuels because it's more profitable than regular grade gas is. The retailer paid about 8 cents more for the premium you pay 15-20 cents more for — though that margin can swing wildly. Refiners make a few cents a gallon more on premium than on regular when they sell to wholesale distributors.

The best rule of thumb here is to consult your owners manual. If the manual recommends running regular, run regular. If it is designed for mid grade or premium, run that. Running a higher octane than necessary isn’t a treat for your engine. That is a long running myth that has refused to die.

 

I drove from Virginia to Kalifornia in late October to come to my new base out here in the middle of the desert. Which makes me curious, why are you coming to CA, if you are coming to Edwards AFB and are military we should hang out when you get here... ie. I need more Jeep friends to wheel with and tow my broken rig home.

I had a bad fuel pump the whole way and was having surging issues below 1/2 tank, so solution. I filled up at 1/2 tank every time, or 140 miles. Basically I calculated miles driven by gallons at each fill up and I averaged 19.5 MPG, I know not completely accurate but driving the I-40 most of the way gets you about that.

>.> not to self after Arkansaw all the adult stores vanish and you are mostly going to listen to Country or Pop on the Radio, well actually you will spend most of your time changing radio stations because you will fly through states too fast.

So not sure if there is science but it seems keeping your tank 1/2 full or more causes your fuel pump to have to work less, and increases performance? At least thats what I saw.

Happy 2,700 miles of driving. VA to TN to OK to AZ to NV to CA, those are the states I stopped in, finished the trip in 3 days. I wasn't towing though, and I have no after-market mods to my engine.

 

Ya but AKI takes into account the Research Octane Number, which has a direct correlation to % of iso-octane (RON of 90 = 90% iso-Octane). Yeah the major difference is how stable the mixture is, but the higher the AKI does infer how much Octane is in the fuel mixture (Gas in Canada and U.S is a mixture of more than 100 different chemicals). And when the mixture has more Octane it IS a Little higher in energy, but in an engine that's less than 50% efficient at converting fuel to energy (MOST internal combustion engines), the difference is very negligible since most of the other percent of the fuel mixture is also things that burn. Regardless though, running higher grade of gas will result in higher MPG, I worked it out once (I travel over 1000 Km's on a roadtrip at least twice a year) and it costs me one cent more per Kilometer to run high grade gasoline than regular, and when it gets me sometimes close to 100 Km's extra per tank, and is better for the environment, I don't mind at all. BUT that's just my opinion to run high grade gas, if you want to stop less for gas than you can run high grade gas.