The manual says 87, that's what I was doing for the first 30K miles, getting about 34mpg average. Recently I switched to 91, and getting about 37mpg with the same commute, so it seems to pay for itself. Does this story sounds familiar ? Are there any drawbacks with using 91 ?

Honda Fit 2009 base automatic

 

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HAHA... Hes eating pop corn because most here are about to tell you to simply use the search. This is not a new discussion. Changing to a cooler spark plug yields you more power an mpg. Again, use search or even google will show the threads.

 

 

Let me google that for you

 

!!!

 

To briefly answer your questions:

1. Some have reported similar results from similar experiments (and similar lack of controls). There are reasons to suspect that the ECU will be able to adjust timing with higher octane gas and produce better milage under some conditions. Whether it makes enough difference to be a net savings is far less certain.

2. There are no drawbacks other than the obvious higher cost per gallon. You won't cause the car any trouble or damage. The manual only specifies a minimum octane rating—it doesn't specify a maximum.

 

Owning BMWs for most of my life I always used 91 octane because that was what the manufacturer called for and I would never put anything less into those cars. Honda on the other hand is a much smaller and simpler motor. I was overjoyed when I found out I had to only put in 87 octane. One thing to note is the tripometer seems to be about 3 MPG off in most cases and how you drive your car makes a huge difference. Lower RPM and top speed in 5th gear changes the MPG significantly. One thing I would wonder is if you get less carbon build up in the throttle body and spark plugs using 91 octane. If that is true, then 91 octane becomes well worth it.

 

hmm,octane rating=btu, additives same?hmm...API

 

I'd say, that depends on the gas station/brand. As supposedly, some use more additives (detergent) in premium fuel.

 

Octane rating=resistance to detonation (and hence how high the compression ration can go, how the timing gets adjusted, etc.). The energy content per gallon of gasoline is the same regardless of octane rating. Diesel fuel does have a higher energy density, which is a large part of the reason why diesel engines typically get better milage than equivalent gasoline engines. (Ethanol has a lower energy density, by the way.)

Additive blends may or may not be the same, depending on the gas station/supplier.

 

While I haven't done it with the Fit (and probably won't), with other vehicles I've had including a Honda Accord wagon and sedan, I did notice an increase in mileage when using premium. The problem was that I didn't notice the vehicle running any smoother or better and the difference in mileage didn't offset the addition cost of fuel so I didn't really see a benefit. The Accord wagon had 215k miles when I sold it and it was still running fine and had never had any engine related repairs. The Accord sedan had 200K miles when we traded it and it also never had any engine related repairs.

 

For the first several months I had my Fit I drove very conservatively and carefully. I did about 10 tanks of 87 octane and 10 of 91 octane. I used the fuel buddy app on my phone to record my miles and fill-ups.

I found that I got 4% better mileage on average with the 91 octane, but it cost about 6.5% more. So I was getting slightly better mileage but not enough to offset the additional fuel cost. So I went back to 87 octane.

After those first months I gave into my true nature and started driving my normal way and my mileage went down another 9%. Oh well.