The user manual says that my '12 R58 (n14) can run on 89 or 91 octane gas.

I have used 89 for the last tank and I am registering better gas mileage with no real noticeable performance degradation.

Although I would not want to run 89 all the time (especially when taking the car to the track), I was wondering if anyone else uses 89 and if there are any negative (long term) effects in using the mid-grade gas?

Also, did anyone notice a gain in gas mileage?

 

I just use 91, the price difference is not that much here and I would not want to hurt the injection system or lower my mpg. Unless you are in an area that has only lower fuel grade , know some people in rural Alaska that use 87 and get octane booster.

On my Gen 1 MINI, I always used 91 or higher and still on the same fuel pump and injectors with almost 250K .

I notice a gain when i don't push that gas pedal more and at high speeds

 

There probably was a difference in the amount of ethanol.

89 is usually blended and the pump (87 and 91 are mixed on site to produce an 89 rating). If you are going to the same station then maybe the 91 has more ethanol content than the 87.

 

Here are some websites that may also have information useful to you.
https://docs.google.com/file/d/0B5vA...U1k/edit?pli=1
http://www.fuel-testers.com/state_gu...anol_laws.html
http://pure-gas.org/index.jsp?
and most importantly - http://www.toptiergas.com/

 

Thanks