[masraum]

Originally Posted by Eric Coffey

Higher octane fuels actually have more *potential* energy, but they require higher pressures (CR) to extract that energy. So, it really depends on what your CR is, and the limits of your car's factory "tune". If your CR is high enough, and your ECU allows for agressive-ish timing, then running higher octane can result in better performance and mileage. It typically does in fact on many newer/modern engines, thought not by huge margins. If your user manual calls for a "minimum" octane as well as a higher "recommended" octane, it's probably a safe bet that the latter will give you a slight performance and/or MPG boost.

Also, ethanol increases octane, but also reduces energy/efficiency. It's also not as stable, so the "shelf life" of E-blends is not as long. As such, regular lower-octane fuel can be "proofed up" with ethanol, but that octane rating will diminish much quicker than a non-ethanol fuel. Also, when you see an octane rating at the pump, that is the minimum value with or without ethanol. So, an 87 octane E10 is a blend of 90% 85-octane gasoline and 10% ethanol.

The CR is 10.5:1. I've seen online that the previous 6cyl in the Outback required premium gas which folks complained about so Subaru backed the requirement on this newer (last) 6cyl down to regular.

Originally Posted by Pazuzu

The 92 ethanol free kicks butt for the p-cars, I've been know to drive out there just to fill up. For sure, if my weekend commute took me by there I'd be using it every time.

I think they have 87 ethanol free as well, which would be perfect for the Subaru.

I didn't notice an ethanol free 87, but I'll check the next time that I'm there. That's what I'll use if it's available. If not, then I'll just stick with regular 87.