Car req 87octane, what's better, 92 no-ethanol or 87 w/ethanol?
 

I know that we all hate ethanol gas.

I'm pretty sure that I've got a handle on the fact if your motor requires 87 octane, then using higher octane not only doesn't help, but can actually hurt efficiency (higher octane burns more slowly)

So, if you had a vehicle that only requires 87 octane and won't do anything fancy/special if you put in higher octane, then (assuming comparable additives and quality) which gas is better to use, 87 octane with ethanol or 92 octane ethanol-free gas?

I put some of the ethanol free in the Subaru the other day and about halfway through remembered that the car only requires 87.

I'm not concerned with causing issues, I'm just curious theoretically, which would be a better/more efficient fuel to use.

I know what I'd do with my Honda's if it were me. I'd run the 92 without the ethanol. I think the Honda's will advance the spark to take advantage of the higher octane via the knock sensors. I'd expect better gas mileage too. I've tried hard to avoid ethanol in my cars.
If you're not worried about the effects of ethanol, I'd say it comes down to what your wallet can withstand from the hit in price.

You use reg fuel in your Boxster? I think my Cayman S, requires 91?

Higher octane, no ethanol, preferably "top tier" approved (better/more detergent additives).

Some of my Subaru friends tested this a few years back (serious turbo guys with dynos). My understanding from them is standard Subaru ECUs will not advance timing to take advantage of higher octane fuel. They will only retard timing if detonation is detected. No appreciable HP or MPG gains. These guys build stupid fast machines... but they sound like broken flat fours...

Of course, you could always install software to take advantage of the timing. You would then need to run high octane at all times.

I don't think ethanol is an issue with newer cars (you just bought a new one, right?).

My DD is an E46 wagon that specs use of 92 octane. I've run it a couple times on 87 (like when 92 wasn't available). There is a noticeable difference in power and also less MPG.

Nope, it's the new Subaru. In the boxster use whatever the highest octane available is, which around here is usually 93.

Our Subaru is a flat-6 with no turbo. I wouldn't expect much out of a chip/tune for a non-turbo, and the missus is probably not interested in any weirdness that would probably come from a chip/tune.

On a turbo, I could see some possible benefit (probably requiring a tune). Turbo folks seem to love ethanol.

I have to say, I am loving the 6 cyl (vs 4cyl or now 4cyl turbo). We also seem to be getting about 28-30 mpg on the highway.

Just look in the manual for the octane requirements and use that. No sense in wasting money if you dont have to..

My BMW usually gets 19-24MPG highway on a light foot with 92 (big sticker for premium fuel on gauge). I saw it go down to 16-20MPG using 87.

I'd do a little research of what the oil change interval is for the car and see what the forums say to do. A lot of the newer cars are specifying 10K+ miles. Not sure I'd be following those. Certainly not on a newer BMW.

Non-ethanol fuel will provide a higher density fuel than E10. You could expect a small gain in fuel efficiency but not enough to overcome the more expensive fuel. When I would fill up in Iowa they had a choice of E0/87 and E10/87. The E0 would give 2-3% better economy so it was worth it if the price was less than 3% different. Now they don't so I put whatever crap they have in the tank. E0/92 is far more than 3% higher so not worth it for cars that don't require it.

I'd run the 87 octane and wouldn't look back. I've ran both the 87 ethanol and the 91 no ethanol in a few of my cars and never noticed the difference except in the cost of the fuel.

I had Weber carbs on my car when I lived in Hawaii. The ethanol crap was horrible for the carbs.

A guy that worked for me had a small plane with air-cooled engine. He turned me on to the 76 Gas Station that carried 'marine' gas that was ethanol free! We would go to lunch with two 10-gallon fuel cans for his plane and stop by to get his plane gas.

I started using the stuff for my 911 and it worked miracles.

a new car should be fine with either

OTOH, Houston is very humid...

real question is whether the increment in 'safety' is worth the extra $$ cost - Porsche owners would be expected to be relatively price insensitive

Hmmm. You should get around 10% better mileage on the no alcohol, but is that worth the premium paid? Cindy's Toyota gets 87 gasahol. I run no booze in the Mustang because it's variable factory tune actually delivers more power with higher octane. Says so right there in the owners manual..

I've put it through an 08 TaurusX wagon I drive that gets maybe 21 on the highway. The car never cared one way or the other. Same with my 2012 F250 and my Rav4. I've found that driving style has more effect on mpg than the gas I put in it.

Yeah, ethanol should definitely be avoided on older cars that don't have the fuel system components designed to handle it.
Ethanol is highly corrosive, hydroscopic, less energy-dense, and provides less "lubricity" for fuel pumps, sending units, etc.

It does provide and octane boost to low-octane bases, and runs cooler. So, when used in the extreme (E85, etc.) it can be beneficial for specific-use applications (high-comp. turbos, etc.).
Tuners like E85 which has a relative octane rating well above 100, as they can push the tuning limits where efficiency, reliability, and service intervals are not primary concerns.
Though, it can also present the same unwanted effects of low-octane fuel, via pre-ignition.

So, for everyday use on a non flex-fuel or "tuner" car/engine, I'd pick the non-alcohol option every time, especially within the same octane rating and/or if the ethanol percentage is over 10%. YMMV, literally...

If it is a newer car and doesn't sit for long periods of time, the E-10 will not be an issue.
If it is an older vehicle then avoid ethanol like the plague.
If it sits for a long period stick with the no ethanol gas to be safe. The other option is 87 octane and an additive like Stabil.

Any octane without ethanol.......

Right, this is a 2018 Outback with a H6. The manual calls for 87 octane. 87 octane has more energy than 91-92-93 octane, but then ethanol also, I believe, reduces octane (so is it 87 with the ethanol or is it 87 octane w/10% ethanol).

I'll probably use the non-ethanol 92 for the Boxster when we take that out there, but I guess from now on, I'll go with 87/10 when we take the outback.

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 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.