I'm not sure if Subaru has different tunes for different octanes. I'd have to look at my owners manual and compare it to a newer one. I know we have 93 out here.

 

Back in the early days of having the car in this country, the conventional wisdom was that the factory tune was for 91 octane, since that was the lowest common denominator. Not sure if that's still true or not. It wouldn't really make sense to have different tunes for different parts of the country, since people relocate.

 

I was gonna write that, but I went with what I already posted.

 

Maybe I did put in 93 octane and I've just gotten used to the cars pick up

 

I doubt that would have much of an impact. As stated, not all places (Oregon, for example) offer 93 octane fuel, so the lowest common denominator thing makes sense. That being said, if you put 87 in it for some reason, and then 91 or higher afterwards, you would DEFINITELY see improved performance.

Side note: in Oregon, we are not allowed to pump our own gas, and some imbecile forgot I'd explicitly said Premium, and half-filled it with regular before I noticed. The car ran like garbage for that tank, and once I was back to Premium, it was all smiles again.

 

I've never understood states that don't let you pump your own gas. They let all the dumb asses here in Florida do it.

 

No idea. Believe me, it's dumb.

 

I let Drews pump my gas

 

Depening on your driving style, you would be able to tell the difference between the octane ratings.

I have always tended for agressive driving, and in most cars I have owned, I got better performance out of 93 than 91 or 89/87...even my old '89 CRX benefited from 93 octane.

With a ECU controlled car, higher octane allows the stock tune to sightly advance the timing, giving better performance, and lower octane results in slightly pulling the timing.

 

Knock is the enemy of your engine. Octane is a knock deterrent. The higher the octane, the lesser the knock, the more power you can make. At least that's how I assume it works from the limited knowledge that I have.

 

^yes, exactly what I meant....I was just trying to avoid using that dirty curse word 'knock'

 

Bahaha thanks for the replies guys I'm starting to think its a case of bad gas. I just filled up and I have better pick up so far.

 

Luke wears black to denote his own ambiguity.

A stock car should have no problem with 91. Huge population centers in key markets only offer 91.

I shop for fuel like I shop for Subarus, by price.

 

Higher octane gas is more resistant to knock, which is what causes many engine failures. If you have the chance to use 93, I would, especially with how the newer MYs (your avatar is an '08+) tend to lose engines much easier than previous MYs @ stock levels.

I let Drews pump my ***

That explains a lot...

 

Ive ran both in both of my wrx's over the years didnt notice any difference

 

Correct me if i'm wrong, but isn't octane, simply put, a percentage of a certain type of molecule? My understanding was that it is more or less directly tied to compression. If you have enough of the percentage/octane to resist premature detonation at a certain compression, then you are good and any higher octane isn't really going to benefit you in any way. So I guess, if my slightly drunk and old memory is right, the question is whether our tunes have room for improvement after 91 octane (which is the recommended I believe) built into them.

 

The stock tunes are set up for a specific amount of timing, at a specific compression ration, using a specific fuel grade. Premium, whether 91 or 93 in your area, is what you should use. Our tunes are set up for knock detection, but are not meant to be used with fuels varying in octane rating. FlexFuel vehicles and cars with octane detection methods can and will adjust fueling and timing according to fuel type, but our cars are not designed for it, so the advantages to running higher grade fuel are slim to none.

 

It used to be the ratio of octane to isoheptane but I've since lost the plot and the last time I took ochem was four administrations ago in the stone age.

 

you are partly right.

The octane rating in gasoline is not directly the percent of a specific molecule....it is 'this blend ignites/burns/detonates like a blend being X amount Octane (octane is any of 18 different gases in the methane family which contain 8 carbon atoms) It is also known as 'anti-knock rating' as the higher the octane, the less likely you are to have knock.

As is evident of a stage 1 or 2 car....there is a multiplier in our ECU. If you are running stock tune, with 91 octane, your multiplier is likely lower than if you ran 93 octane, so while there is only one tune, you will likely benefit from the higher rated fuel.

 

what demon said. the octane rating isnt the true rating, whats on the pump is r+m/2. there is also the mon rating and ron rating. so say if that number is 93 your true octane(mon) might be 91. obviously running 93 to 91 makes more of a differance in our cars than it would in a say sentra. rule of thumb is you want the lowest, safe octane your motor is set for. the lower the octane the better the burn, but the higher the octane the better knock resistance, plus better cooling properties. all i know is i wish i had 93, live in cali so we dont even have "real" 91. have the damn acn crap. damn hippie state lol. whats sad is 91 is 4.59 a gal right now and i buy 110(for my bike) for 8 dollars a gallon. i remember when gas was 2 bucks and 110 was still 8 bucks. so in two more years it will prob be cheaper to buy and to tune for 110 then 91 lol.

 

i have 93 and 91 available in Maryland and first off why pay the same price for premium and get 91? so i always stopped somewhere with 93. there was one time I was lazy and just got 91 and i will say my car felt WAY more sluggish for that tank. from that point on i have stuck with 93 and its never happened again. my two cents

 

Your ECU had adjusted itself to run on 93, so it didn't run quite right on 91. If you had run a few tanks through, it would've adjusted and you wouldn't have noticed any difference in your butt dyno. They "learn" the conditions they run under and can make small adjustments for octane, altitude, etc.

 

If I'm reading the OP correctly, the question is will 91 perform better than 93. The answer is no, never, not in these cars on the stock tune. It may perform as well however.