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

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Ethanol has *higher* octane rating than petrol.
It also has lower energy density than petrol.

So there are lot of variables to balance.

Generally, unless car is tuned to specific octane, using higher octane will not net any extra HP. Using petrol only will net higher MPG due to higher energy density though.

5-10% ethanol does very little in modern cars. It only lowers the MPG somewhat. ECU will compensate.

E85 on the other hand, is great for turbocharging. 102 RON.

My DDs over the past two decades (F150 now) get 87 w/ 10% Eth. no issues ever. My 911 and many 2-cycles require higher 93 and Non-E is all they get... forever.... no issues there either.

We are lucky enough to have regular or premium gas no alcohol added. If I am driving a rental I will use the gasohol because it is cheaper with all the government subsidies to make it. I just pay the extra buck and a half per tankful for pure gasoline for my 80s cars. My wife's Macan needs premium, and it gets pure gas only because we plan to keep it long term.

Up until last year, 93 no-ethanol was readily available (although 40 cents more) here at locally owned Smiley stations, but the owners sold all the stations to Sprint, and now it is no more. I have found 1 other independent that carries 91 no-ethanol, but it it very high priced and to be honest, the place looks like a dump. I hate to imagine what the bottom of the storage tank looks like.

Quote:

Originally Posted by Eric Coffey (Post 11142759)

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.

Quote:

Originally Posted by Pazuzu (Post 11142760)

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.

Quote:

Originally Posted by SiberianDVM (Post 11142948)

For many years in our old home, I went to a nice looking Chevron for gas. I eventually noticed all of the cars running less than optimally. It never clicked or occurred to me that it could be the gas. One day I was running low and wouldn't be able to get to that station and stopped at one of the super cheap chains, like racetrack or something like that. I almost immediately noticed that whatever vehicle I was driving at the time ran better. I haven't been back to that gas station since. I'll go anywhere else. I don't know if it's because the tanks leak or if they are one of the stations that you hear about where the owners "top up" with water or what. I'll go with Hanlon's razor and assume it's stupidity/negligence vs greed/maliciousness.

I drove my turbocharged (and DIY-converted) cars on E85 for 7 years. Unfortunately, government is not subsidizing it any more so it is not worth it.

But I could run more boost, have more aggressive ignition and produce more torque on E85 than on gas. E100 would be perfect from power perspective, (but tricky in cold weather).

The station I use for all local gas purchases is a 1/2 mile from my house. They have two pumps that are pure gas, and one that has either real gas or gasohol. They recently replaced al the tanks due to regulations. They sell COLD beer, and have Conoco gasoline. I have always liked Conoco as they were started in Ponca City, OK. They merged with another Oklahoma company Phillips 66. They moved to Houston several years ago. They make good gas.

Quote:

Originally Posted by beepbeep (Post 11143072)

Ethanol is less energy dense, but it can produce more power. Mileage sucks though in that case because you run it much richer to produce that power.

In testing E85 had about 65-70% the range of E0 in the same car, same driving conditions. But the 0-60 was .1 second quicker with E85.

Quote:

Originally Posted by masraum (Post 11142995)

The CR is 10.5:1.

That is certainly high enough that you should realize power and MPG benefits with higher-octane fuel. Of course, it depends on the specific vehicle's ECU mapping/sensors to take advantage of it. Id imagine a newer Subaru would be able to go a bit more aggressive on the timing to give you a slight boost. The HP may not be noticeable, but if you carefully track your mileage over several tanks, I'd be surprised if you didn't realize a couple more MPGs with 91+ over 87 (again, non-ethanol). As a bonus, the higher-test stuff should cause less oil dilution, and has a higher concentration of add-pack (detergents) as well. Though, I usually run a bottle Techron towards the end of oil change intervals anyway.

Quote:

Originally Posted by masraum (Post 11142995)

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.

Yeah, if you don't want to bother with the higher-octanes, I'd still try to avoid E10 87 whenever possible.