Assuming you have a flex-fuel tune maybe...Id rather just use gas but we don't have ethanol free in Taxachussetts

Nothing to do with the tune really. Just the added knock protection.

That's not exactly what it says. You can use 91 as long as you want.

Note that if you're at a high elevation (in the mountains), 93 octane will almost certainly not be available. That's because at higher altitudes, lower air density makes higher octane unnecessary to prevent knock.

the higher the octane the better. But if you can get shell or bp 93 go with them first.

Shell 91 with vpower for the air miles that I will never use.

For some strange reason, My OFT tune doesn't like Chevron 94 gas as much as 91 Shell according to my data logs...maybe it's the quality of gas.

Funny thing is mine work well on 93 oct, but non ethanol blend and logs looks pretty good

I initially used Chevron 94. Decided to try Shell 91 awhile back and stuck with it since. Gas mileage improved (taking the same route to/from work everyday) and the engine just seems to feel happier with it.

Remember, ethanol is actually an octane booster. Some 94 fuels have it for that purpose.

Once you get above a certain altitude, most gas maxes out at 91 because at altitude the effective compression is lower. Utah, Colorado, most of New Mexico are places where anything above 91 octane is rare.

I use 91 octane non-ethanol which silences my crickets and gives marginally better mpg.

Yup, when I'm somewhere that it's an option I do too. I don't like paying the extra $$ for it but it does help the car to run better. I wouldn't mind if it was available less than 50 miles from home though :sigh:

I'm using 91 from Shell. Nothing problems appear. I couldn't find gas station where have 94 near my home..

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Is this a MON or RON rating? US usually posts (RON+MON)/2. It matters.

I think this is the only accurate way to know the quality of fuel. Data log constantly and know how much ignition advance and knock you typically get during certain ambient temps.