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Part of what you paid for is good fuel economy. Fuel economy is how much you pay for fuel. How much you pay for fuel depends on what fuel you buy and how much fuel you use. To achieve better fuel economy, Subaru designed the car to use the cheapest commonly available fuel.


My GTO, with cam/heads/stroker/tune, requires 93 octane. My Impreza does not.
 

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Since it's been discussed in the "Anyone do any Mods yet?" thread, I was curious to see what type of gas you use in your Impreza?
I have a 2017 Impreza 2.0i sport and I’ve been filling up with 87. I was wondering if there’s be any affects if I started pumping her with 89 rating. Would it be a wise decision? (I know I’ll be spending more) (just wondering if itd help with performance)
 

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I have a 2017 Impreza 2.0i sport and I’ve been filling up with 87. I was wondering if there’s be any affects if I started pumping her with 89 rating. Would it be a wise decision? (I know I’ll be spending more) (just wondering if itd help with performance)
Probably will not make any difference other than you feeling the placebo effect of having spent more at the pump.

Our Imprezas take 87 octane. Period. No performance boost from higher octane unless you did some mod to your engine.
 

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Where would one find ethanol free gas? Is the pump a different color like diesel or E85?
there's a website and app called pure-gas that keeps track of where you can find it. (can't post links yet)




Ethanol free will get slightly better gas mileage. Higher octane is often ethanol free. how much better gas mileage? doing your own math will be required to see if the mpg vs price trade off makes sense. So go for the higher octane not so much for the octane, but for the ethanol free.

I always had older vehicles and after having to replace an o-ring on a fuel pump in below zero (which i unscientifically attributed the failure to ethanol) switched to always using ethanol free gas, even higher octane than what's called just to get that slightly better gas mileage. I felt that cars built in the 80's and early 90's just didn't have the parts designed to deal with ethanol long term.

So my way of validating running expensive gas to myself was to make it about running ethanol free to reduce the risk of o-ring failures, get slightly better gas mileage, store longer in my seasonal vehicles, and be ok with spending more to do my part in anti-ethanol subsidization consumerism.


But now that I have a brand new vehicle whose parts have been designed after ethanol has been popular for years, i feel like i have less to worry about ethanol causing failures in soft parts of the fuel system. I will have to do some maths and average out the mileage between 87 and 91 ethanol free to see if it makes financial sense now to go with the higher mpg gas at the higher price.


Everything I just said against ethanol goes out the window for running turbo performance motors where octane is king, or tuning for e85, or flex fuel vehicles.
 

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Ethanol free will get slightly better gas mileage. Higher octane is often ethanol free. how much better gas mileage?
True - ethanol-free gas will yield better gas mileage and tons of documented proof. Ethanol is actually not very good for an engine at all and reduces performance.

False - Higher octane fuel is not "typically" ethanol-free

Just about all fuels nationwide have about a 10% blend of ethanol. There are special pumps, in many states that I have traveled to on business, that offer 100% ethanol-free gas at an extremely high price (like $1.00 more/gallon in many cases) which makes it unrealistic to purchase as the gains in mileage and performance do not outweigh the high cost.

I have a 2017 Audi and a 2017 Forester XT that both "require" 93 octane and all high-octane fuel I have ever seen is still an ethanol blend.
 

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Many people do not realize that HIGHER octane basically means SLOWER burning. (higher flashpoint and more controlled burn-rate)


Higher octane does NOT mean there is more energy in the fuel hence does NOT make more power by itself.
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On the other hand... with diesel fuel, we measure CETANE which is a measure of how much energy is available in a unit of fuel. This is why adding a cetane-booster additive to diesel fuel actually adds power and improves MPG.
 

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False - Higher octane fuel is not "typically" ethanol-free
Eh, I have data to back me up.
Well at least here in the midwest. (corn belt) Look at all the 91's (name brands)

https://www.pure-gas.org/index.jsp?stateprov=MN
https://www.pure-gas.org/index.jsp?stateprov=WI
https://www.pure-gas.org/index.jsp?stateprov=IL
https://www.pure-gas.org/index.jsp?stateprov=IN

New york Too.
https://www.pure-gas.org/index.jsp?stateprov=NY

But get into the oil belt states and I see the trend reverses.
I will cede the point that that will vary by region.
 

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I use high test all the time. The guys at the dealer said it was good for the car when I asked. The car runs much better.
 

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I use high test all the time. The guys at the dealer said it was good for the car when I asked. The car runs much better.
Anything more than 87 is a big waste of your money. The car was designed to run on 87...anything more is NOT beneficial. The "guys" at the dealership you are speaking with are morons. Do a bit of research and you'll find that what I am stating is 100% accurate. If the car runs "better" than it is all in your head and seat of the pants meter to justify you paying 50 cents more a gallon for NOTHING:wink2: The additives are similar and, with a DI engine, it doesn't matter much anyway as the fuel does not wash over the valves. A bottle of Chevron Techron every 3K miles will keep your injectors clean but is also unnecessary if you use a quality fuel that has the additives already in there.

Save your money and invest it elsewhere. 91-93 octane is a BAD investment.
 

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Higher octane gas actually has less energy per unit, so unless your engine is specifically designed to run on it the chances of you getting better mileage is extremely slim / all in your head.[/QUOTE]

In some cases you will get worse mileage with Premium. A few years back Arctic Cat required 87 octane for highest power output.
 

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Little info about ethanol free gas (that I learned last year). If you are a homeowner you no doubt have a ton of little engines around your garage. Lawn mower, snow blower, chainsaw, weedwacker etc.

When you use gas with ethanol in them the ethanol will actually eat away at the materials used to make the carburetors in those little engines. I had a small engine repair guy come and go through all of my stuff for me and he said it is the most common problem people have.

I went out and got pure gas and put them in my machines and they all run MUCH better.

Modern day cars are made to use ethanol and won't get damaged from it.
 

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I am commenting on this SUPER late...but I still haven't really gotten an answer after reading all the comments.... hah!

Soooo....regular or premium? I put regular in it, but this last tank I got from Costco is making my car run a tad rough.
 

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Could be a bad tanks worth or something else going on. I've personally stopped using Wawa gas stations for a similar reason. Regular 87 from them made the idle rougher and the car just wasnt as smooth when driving. Regular 87 from other local stations seems to change that for me and just don't use Wawa anymore. It may be the cheapest around by a few cents or so, but there is a noticeable difference and I wonder if Costco fuels fall into that type of category. Or it's just a bad tank, it happens.
 

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I had worse gas mileage with costco 91 vs costco 87. Will stick with 87!
 

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I use 87 octane in the Impreza and ethanol free in yard equipment. I found a station with ethanol free by asking google where I could find it. It found a website listing a number of places that sold it and one was only about 10 minutes away.
 
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