Sonic Boom NH

I would say it’s a fluke until you can prove it with accurate data. If you really want to know if you’re getting better mileage from one octane or the other you need to do an accurate study to collect enough data to make an intelligent decision.

To do so what you want to do is collect data for 10 tank fill ups of 87 and then collect data for 10 tank fill ups of 91/93.

Take your mileage from each tank fill up of 87 and average them, then take the mileage from each tank fill up of 91/93 and average them. Once you compare your findings then and ONLY then will you have an accurate answer from the data and no fluke…

Do NOT do one take of 87 and then another of 91/93 and then back to 87 etc. Do all 10 of 87 one after the other, then do 10 of 91/93 one after the other. What you should do is after your 10th tank fill up of 87 is fill up with 91/93 and DO NOT use the data from that tank to insure you cleared all the 87 out of the tank. So what you will end up with is actually burning through 11 tanks of 93 disguarding the first tank of 91/93 data.

jt14894

My car got crappy MPG during the first 1,200 miles since I was still breaking it in.
During that time, it averaged less than 20 MPG, but after that, MPG went up.
My car has just over 10,000 miles and its been getting anywhere between 22 to 23+ MPG in 50%city 50% hwy driving, using only 87 octane.
At my most recent fillup, a few days ago, I put in 15.085 gals @ 362.9 miles. This was good for a calculated average of 24.057 MPG in 60% city and 40% hwy driving.
Not too shabby. Woo hoo!

siggy14

Also on this data collectiong you need to make sure you drive the same route, same amount of traffic and stops and go type situations every tank full, if not there is just to much that can change how much MPG you will get.

Diabolical!

I'll put it in words we can all understand. Simply filling your tank with a higher octane WILL NOT increase mileage. If you got better mileage with this tank, then you would have gotten better mileage even if you had filled up with 87 again. Attribute it to slight changes in driving and break-in. If you want to benefit from a higher octane, you MUST get a tune.

RCT06GT

My MPG's keep getting better and better. Maybe because I am not punching it as much anymore. I am coming up on 3,500 miles and im averaging about 18 or 19 MPG's with about 80% city driving and 20% highway. School then work. With the occasional thursday night track.

Arrow

From what I've heard, you need a different tune to get the engine to properly use the higher-octane gas. Far more engine-savvy people than I have told me this, so I'm stick'n to it. Makes sense, and since I can't gather accurate enough data to prove it by driving, I'll stick to what makes sense.

RCT06GT

Try the tune, you will like it.

Warlok

Skunkworks said it all. He is right, plain and simple. Get the tune, or run 87 octane.

wakebord99

NOT TRUE

I just did it myself. I have a new car (1100 miles) and until I put premium into the tank on Saturday the BEST i ever got on my daily route was 14.5 MPG and this was fairly concervative driving. After reading this i decided what the heck, i'll give it a try. Filled it with 93 octane, reset my MPG indicator (which i do every time i fill up) and did my daily route every day for the last 3 days. I have been driving VERY aggressive for the last 3 days and have averaged 16.2 MPG. Not as much of an increase as mentioned above, but in actuality driving style for driving style i usually get about 13.7 MPG, so it's about an increase of 2.5 MPG.

Now i understand the difference between 93 and 87 octane as good as anyone if not better. I understand that 93 octane basically just allows your car to run a more advanced timing over the stock 87 octane. But I really wasn't expecting this drastic increase in mileage. Also note that my corvette 99' could run on 87 octane, but drastically reduced power and much worse MPG.

Don't try to convince me that it's breaking related because my MPG hasn't changed but .2-.3 if that between fillups since I got the car, and now i'm seeing 2-2.5 increase on the same exact route averaging the same exact 33 MPH.

HDmstng

Well I ran through that tank of premium and decided to just go ahead and fill up with 87 octane. Low and behold, the milage increase I had observed did not drop off. From what I assumed, the milage increases that could be expected would have occured in small increments, not a 3 mpg jump. Since I was right at 800+ miles, now over a 1000, and the manual stated not to try and calculate milage till after a 1000 miles, could this have been programmed into the car? The manual also states there is no break in required, could it be there is some sort of programming that kicked in based on miles driven? The programming could break the car in for the first 800+ miles, and then a milage boost?

Did anyone else notice a jump of 3 mpg after 800 miles?