Available locally is Premium Unleaded ETHANOL FREE 91 Octane or Premium Unleaded 10% Ethanol 93 Octane.

Would you choose 91 Octane ETHANOL FREE or 93 Octane 10% Ethanol?

91 ethanol free.

All other factors being equal, ethanol free all day long.

It depends on what you drive. Most vehicles use 87, 91 would be a waste of time. Also, I would go with the octane recommended in the owners manual. If given the choice, I would stay away from Ethanol.

Depends on the vehicle. My Jeep gets the cheapest stuff I can find, my GTO gets top tier premium, and all lawn equipment gets ethanol free. You don't get any benefit from higher octane in an engine not built for it, so it would be wasteful to get a higher octane if you don't explicitly need it.

With prices around here, the ethanol gas is cheaper per mile than the 100% real gas too, so no real point in buying it if you don't actually need it.

Ethanol is pork-barrel political bullshit, in addition to being bad for my older vehicles. If I had a choice I would absolutely buy non-ethanol fuel. Unfortunately I have no choice, which is ironic since I live on the fringe of the Permian Basin of west Texas, one of the biggest petroleum producing areas in the US.

91 sans ethanol would be my choice although I'd need to evaluate the cost difference as only the no ethanol would contribute much to the performance. I could purchase a custom tune for my Taco which would take full advantage of the higher octane as well as offer a more aggressive shift sequence, but's hovering around $1000 so not in the cards for me.

Ethanol free, if you can find it.

There is an APP for station locations:

"PUREGAS"

Ethanol and octane don't go together in that performance is interdependent. One doesn't make up for the other. It isn't a trade off.

I would prefer to get non-ethanol gasoline for any car, regardless of what octane rating it needs. No ethanol does put more energy in any given amount of fuel. It is more powerful than 10% ethanol fuel. As someone else said, though 100% gas is very expensive, if you can find it, that you pay more per unit of energy for pure gasoline than you do for ethanol laced fuel.

I would get the octane rating that engine needs to avoid predetonation. That is what octane does - it prevents the fuel/air mix from igniting early in higher compression engines. It doesn't make the gasoline have more "power" or give the engine more power. You use higher octane gas if the engine needs it. If you don't need it to stop pre-detonation (knocking), it doesn't do you a bit of good to use higher octane gas, and only wastes money.

My car has a medium compression ratio - higher than most cars, but not as much as a performance car. It was built that way so that higher octane fuel would not be needed. In Japan, the same engine has a higher compression ratio and higher octane is definitely needed. (Apparently the Japanese don't mind paying for hi-test.) If I put high octane fuel in my car, I would just be blowing money out the tailpipe for no benefit. It runs fine on regular and adding octane wouldn't add anything.

Whatever octane the vehicle calls for. If it calls for 93 use the 93 if it calls for 87 I am guessing the price difference in 87 and 91 Ethenol free will completely negate any gained mileage.
Ethenol hurts mileage but not the vehicle much anymore.

Small engines on the other hand are destroyed by ethanol. I gladly pay the higher price for ethanol free for my yard equipment.

I used a few tanks of ethanol free in my Explorer and the gained mileage did not make up for the price increase and the added drive to the lone ethanol free station.

Corn is not for cars. Corn is not for cows. Corn is for popping (not in the microwave) and stew and best left on the cob.

If you look at an E-85 fuel compliant vehicle, notice the fuel economy is rated using real gas. Not corn gas. Using the E-85 gas reduces observed milage by 40%. Using corn gas in your car drops milage by 4% or so.

The corn gas particles are more coarse of a product and causes premature wear on fuel pumps, injectors, etc...

Corn gas also absorbs moisture from the atmosphere more rapidly and rusts out the bottom of the gas tank, fuel pressure regulator, etc... This is why you will never see corn gas for sale at a pier, dock, or nautical establishment.

There is also the double subsidy for corn gas. Other than that, it is great!

I ran a couple tanks of 100 octane AV Gas in my Ford F150 in attempt to pass the Florida emissions test back in 90's. The numbers were good but I still failed because my cat converter was removed. The truck was definitely peppier!

We have a car that says it wants 93 octane gasoline. I’ve yet it see anything higher than 91 offered for sale out here. Exxon seems to reliably sell ethanol-free 91 octane fuel; 85 and 88 octane have some level of ethanol (and yes, for some reason, Exxon sells 88 rather than 87 here).

quote:

Originally posted by TMats:
We have a car that says it wants 93 octane gasoline. I’ve yet it see anything higher than 91 offered for sale out here. Exxon seems to reliably sell ethanol-free 91 octane fuel; 85 and 88 octane have some level of ethanol (and yes, for some reason, Exxon sells 88 rather than 87 here).

If it doesn't knock at 91 octane (and I bet it doesn't), don't worry about it.

jhe888 explained it well.

quote:

Originally posted by TMats:
We have a car that says it wants 93 octane gasoline. I’ve yet it see anything higher than 91 offered for sale out here. Exxon seems to reliably sell ethanol-free 91 octane fuel; 85 and 88 octane have some level of ethanol (and yes, for some reason, Exxon sells 88 rather than 87 here).

I wouldn't worry. Cars today can detect knocking and will adjust the timing/fuel/air mix to compensate if needed.

Some of today's variable valve timing engines(Honda's Vtec or whatever they have now) will have a second set of lobes on the camshafts. When you go above a certain RPM the second set opens the intake/exhaust value longer letting in more air. This will often create a higher compression. Some of these engines really only need the higher octane gas when you get past a certain RPM anyway.

Just use what is recommended if the car is stock. Some newer cars that run on 87 can be tuned to pull more power from higher octane fuel but at a cost.

Does your vehicle require premium fuel of 91-93 octane? If not, and it is set up or rated for just 87, I think it unlikely you will get any better performance on the premium.

quote:

We have a car that says it wants 93 octane gasoline. I’ve yet it see anything higher than 91 offered for sale out here. ...

You give your location as Wyoming. Wyoming's high elevation (its lowest is still over 3000 feet) creates less cylinder pressure and the octane rating can be lessened with no problem.

quote:

Originally posted by egregore:

quote:

We have a car that says it wants 93 octane gasoline. I’ve yet it see anything higher than 91 offered for sale out here. ...

You give your location as Wyoming. Wyoming's high elevation (its lowest is still over 3000 feet) creates less cylinder pressure and the octane rating can be lessened with no problem.

Yeah, pretty familiar with that

How much more is the 91? If only a few cents more I'd use it. Most likely the 93 is the exact same gasoline as the 91, only with 10% alcohol added to raise the octane 2 points.

I'd use the 91 ethanol free, which is exactly what I use in my Mustang. If I actually needed a higher octane, I would mix in some race gas before I would put in an ethanol fuel. My truck on the other hand gets whatever is pumping.