Originally Posted by matmatician
I've never put anything but top tier gas in my new engine, and its all been 87 octane. It averaged about 32 MPG on the drive to and from Oregon from the Seattle area. I'll fill up with premium next time I go on an extended drive and see what happens. I was under the impression that certain engines were designed with certain octane ratings in mind, and that the car wouldn't gain from higher octane? And that it may even act funky if you do? I'm sorry for being a newb here, but I really haven't researched gas that much.
Since you have the older engines with their lower compression ratio it wouldn't benefit from higher octane. The 2012 on the other hand has a 12:1 Compression ratio, Twin-independent variable valve timing that can advance or retard timing within the limits of the computer programming. People are also hanging onto the theory that the 2.0L GDI Ti-Vct will advance the timing up to the incipient knock limit, and that higher octane will provide better performance.
87 octane is the minimum octane rating required, but in mountainous states where 85 Octane fuel is available it would be recommended that you do not use such substandard fuels.
I would believe that higher octane fuels would provide enhanced performance, however if it would also improve fuel efficiency I'm not as certain, as I have yet to run anything other than 87 octane E10 from the local BP station after the initial factory fill of 5 or so gallons + the remainder of the fuel that the dealer put in at delivery.
I also still have less than 1800 miles on the car. I might consider experimenting after 2000 miles, but it would depend on the additional cost. Theoretically at $0.2 more per gallon it would cost $2.5 more per fill up if a full tank was required between 87 octane and 91 or 93 depending on what's available here. Too bad I don't know of any stations near here from which to find E0 gasoline.