What grade gas do you use.

[Spuds]

Originally Posted by Tcoat

No it doesn't it says 91 which is still premium.


I don't think the OP understands what the numbers mean and feels that it is just a quality thing. It is not.

My understanding may be imperfect, but the main affect low octane gas has is that if you ignite too early, it creates too high pressure near the cylinder walls, resulting in detonation. The Subaru ECU good at protecting the engine from this by pulling timing. The result is lower efficiency and power. My understanding is that the factory tune is borderline for not pulling timing with 91. It will pull timing with 87.

I guess it's questionable whether it can pull enough or whether 87 also introduces pre-ignition detonation. I guess someone could log some driving with 87, but anyone who can do that probably doesn't want to (including me lol).

[Borchert97]

Originally Posted by PetrolioBenzina

Needs a tune for ethanol, using the OFT. Surprisingly strong running, and probably how it shoulda/coulda come from the factory.

Huh, it was my understanding that most high compression engines could run on 105 octane race fuel no problem. Am I perhaps thinking of a non-ethanol 105 octane?

[qcbaker]

93, since that's what the manual recommends and its available at the gas station near my house.

[Brink]

Originally Posted by Spuds

My understanding may be imperfect, but the main affect low octane gas has is that if you ignite too early, it creates too high pressure near the cylinder walls, resulting in detonation. The Subaru ECU good at protecting the engine from this by pulling timing. The result is lower efficiency and power. My understanding is that the factory tune is borderline for not pulling timing with 91. It will pull timing with 87.

I guess it's questionable whether it can pull enough or whether 87 also introduces pre-ignition detonation. I guess someone could log some driving with 87, but anyone who can do that probably doesn't want to (including me lol).

I'd imagine there's an upper RPM limit somewhere below redline where there's just not enough time left for the ECU to pull timing enough for 87. Not that anyone would be particularly eager to find where that is.

[Tcoat]

Originally Posted by Spuds

My understanding may be imperfect, but the main affect low octane gas has is that if you ignite too early, it creates too high pressure near the cylinder walls, resulting in detonation. The Subaru ECU good at protecting the engine from this by pulling timing. The result is lower efficiency and power. My understanding is that the factory tune is borderline for not pulling timing with 91. It will pull timing with 87.

I guess it's questionable whether it can pull enough or whether 87 also introduces pre-ignition detonation. I guess someone could log some driving with 87, but anyone who can do that probably doesn't want to (including me lol).

Your understanding is correct. However, some gas stations are not actually giving you the octane that is rated on the pumps. Stations with high turnover will usually be there but since the octane levels drop with age you can be at risk if using rated 87. It could actually be 82 or 84 and since the difference between the small changes in numbers is significate that is serious. The chance of serious pre ignition in a high compression engine increases. Will it pull timing in time is anybody's guess but you most certainly have some bad knock while it does. Could possibly (probably?) use it for the life of the car and never have an issue or you could blow the engine up from one tank of bad gas. I have had to put 87 in a couple of times and it is not big deal but it is not a risk I would accept on an ongoing basis just to save a couple of hundred bucks a year. I seriously question the claimed savings of $2,500 since you would have to go through a shitload of fuel. Ironically you would get worse mileage running the 87 anyway so any savings you think you are getting may be null.




Gonna say something I never do but...
If saving money by using the wrong fuel is that important than people need to be looking at other cars.

[Tcoat]

Originally Posted by Borchert97

Huh, it was my understanding that most high compression engines could run on 105 octane race fuel no problem. Am I perhaps thinking of a non-ethanol 105 octane?

They will run on it but it will serve zero advantage unless tuned to take advantage of it. Higher octane does not mean "better" burning or higher quality. In fact it does the exact opposite as far as the burning part goes.

[finch1750]

I get knock correction on 91, would never run anything less. I run on E85 most of the time now but changed during this last "cold snap" when it was hard to start in 30F temps. Plus I have to drive 15-20 min away to get it so is a hassle to begin with, but worth it for my engine to run better.

Originally Posted by Borchert97

Huh, it was my understanding that most high compression engines could run on 105 octane race fuel no problem. Am I perhaps thinking of a non-ethanol 105 octane?

ethanol has different flow requirements then regular fuel so it requires a tune.

[Borchert97]

Originally Posted by Tcoat

They will run on it but it will serve zero advantage unless tuned to take advantage of it. Higher octane does not mean "better" burning or higher quality. In fact it does the exact opposite as far as the burning part goes.

Makes sense, thanks.

[finch1750]

Originally Posted by Tcoat

I seriously question the claimed savings of $2,500 since you would have to go through a shitload of fuel. Ironically you would get worse mileage running the 87 anyway so any savings you think you are getting may be null.




Gonna say something I never do but...
If saving money by using the wrong fuel is that important than people need to be looking at other cars.

Figuring 30mpg to be nice it's a savings of $600-650 based on the normal $0.20 savings from premium to 87

[Tcoat]

Originally Posted by finch1750

Figuring 30mpg to be nice it's a savings of $600-650 based on the normal $0.20 savings from premium to 87

Well they we go then.

[gravitylover]

93 unless I find non ethanol gas then I use it, I've never seen it over 91.

[RL_BRZ]

93 Sunoco...

[Tokay444]

Originally Posted by gravitylover

93 unless I find non ethanol gas then I use it, I've never seen it over 91.

Why non ethanol?

[Sapphireho]

Originally Posted by Borchert97

Huh, it was my understanding that most high compression engines could run on 105 octane race fuel no problem. Am I perhaps thinking of a non-ethanol 105 octane?

There are places here and there where I live where you can get a variety of different race fuel octane levels from 98 to about 110. You won't notice any difference in your street car, except maybe an increase in acceleration due to the weight loss in your wallet.