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Old 10-20-2013, 11:36 AM   #1
jay bee
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Default Engine mgmt adjust for higher octane? 2013 n/a Sport

2013 Impreza Sport. In the owner's manual it says 87 octane or higher. Is the computer doing anything for HP or torque changes if higher octane is used?
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Old 10-20-2013, 11:47 AM   #2
ToneWrx02
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From wjat i read too high of octane will actualöy start resulting in loss of power.
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Old 10-20-2013, 12:33 PM   #3
lymphomaniac
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It's not really so much about the octane number; it's more about what they put into the fuel.

Or, in different terms: the computer will adjust for different octane fuels (ie. advance or pull timing depending on whatever knocking it detects), but whether you lose power or torque depends on the fuel composition.

FWIW, I'm currently on my 2nd tank of 94 octane (zero ethanol) fuel. There's less apparent fuel consumption based on the first tank of 94 vs. the last few tanks of 91 octane (with unknown - but definitely existing - ethanol content). No detectable difference in power from my butt dyno.
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Old 10-20-2013, 01:25 PM   #4
jay bee
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Quote:
Originally Posted by ToneWrx02 View Post
From wjat i read too high of octane will actualöy start resulting in loss of power.

True if no other changes are made. Higher octane is harder to burn. But if the computer adjusted the spark timing, fuel mixture and possibly cam position for it, there would be more power and/or torque.
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Old 10-20-2013, 01:35 PM   #5
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Quote:
Originally Posted by lymphomaniac View Post
It's not really so much about the octane number; it's more about what they put into the fuel.

Or, in different terms: the computer will adjust for different octane fuels (ie. advance or pull timing depending on whatever knocking it detects), but whether you lose power or torque depends on the fuel composition.

FWIW, I'm currently on my 2nd tank of 94 octane (zero ethanol) fuel. There's less apparent fuel consumption based on the first tank of 94 vs. the last few tanks of 91 octane (with unknown - but definitely existing - ethanol content). No detectable difference in power from my butt dyno.
So the computer will dial it for the knock sensor? I am pretty familiar with gasolines, they are really about the additive package, much like motor oils these days. Interesting about your car. Every now and then I put in 89, no detectable difference to me.

I am a new Subie newbie but not new. I worked on a lot of cars in the 70s to the 90s. DIY until past couple of years, now I just pay good people and do my own stuff once in a while. And I did have a 79 Subaru hatchback 4wd 20 years ago, hated it. LOL
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Old 10-20-2013, 03:00 PM   #6
lymphomaniac
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I actually ran 87 for the first 10 or so tanks, and 89 for the next 10 or so after that. I'd been running 91 for the 30 or so tanks preceding my switch to 94. Not sure if that matters.

My butt dyno tells me that the car on 91 was definitely more peppier than the car on 87 or 89. It also consumed less fuel for the same distance travelled. For both of these points, I blame the ethanol content. 87 was supposed to have up to 10% ethanol; 89 had perhaps less. As mentioned, I couldn't discern any power or torque difference between 91 octane and 94 octane, but I'm only 2 tanks into 94 octane.

On a side note, I used to have the hard-starting issue when running 87 and 89 octane. It pretty much disappeared with the 91 octane fuel. I blame the ethanol content.

Not sure what area you're in (you might want to update your profile ). Here in Canada, we have a trim level called the "touring package", which translates to approximately the premium trim level in the States. Pretty sure the engine and computer are the same configuration for all trim levels, though.

Did I mention I blame the ethanol content?
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Old 10-20-2013, 05:54 PM   #7
jay bee
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I hear you on the ethanol content... Maryland - just starting to cool down now, my nose has not detected winter blend fuel yet.
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Old 10-21-2013, 08:40 AM   #8
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Quote:
Originally Posted by jay bee View Post
Higher octane is harder to burn spontaneously ignite.
High octane burns just fine once you light it. Like, say, with a spark plug.
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Old 10-21-2013, 12:46 PM   #9
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In Minnesota it's completely impossible to find any gasoline without ethanol as far as I know.

I've found one station and the premium (non ethanol) was $1.50 more than regular which is bull**** and not worth anything.
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Old 10-21-2013, 12:48 PM   #10
Angelus911
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IMO buying anything over 87 is probably just the placebo effect and not worth the extra money. If we're talking about ethanol free gas, then that's a whole other discussion...
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Old 10-21-2013, 01:26 PM   #11
lymphomaniac
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Ethanol belongs in my drink, not in my engine.
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