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View Poll Results: The best octane for stock 99 Forester S 2.5
87 33 61.11%
89 7 12.96%
91 12 22.22%
ULTRA 94 2 3.70%
Multiple Choice Poll. Voters: 54. You may not vote on this poll

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Old 05-11-2008, 06:31 PM   #1 (permalink)
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Default What octane to use

Hey i just got my forester, I've heard there 10:1 compression ratio.
To me that seems high so would i get better mpg and or better performance from higher octane gas, 89,91 or even ultra94... i work at sunoco lol
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Old 05-11-2008, 06:41 PM   #2 (permalink)
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Especially if you have a turbo..nothing less than 91. If I could get 93 around here, that's all that would go in my car (we don't have 94 that I've seen). Oklahoma sucks for good gas. I get MUCH better gas mileage on 93. I've never even had a tank of less than 91 in my car.
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Old 05-11-2008, 07:33 PM   #3 (permalink)
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use the recommended octane for the car that subaru says. i believe it's 87. please someone correct me if i'm wrong. anything else and you're just wasting money.
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Old 05-11-2008, 07:39 PM   #4 (permalink)
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Default 87 octane is fine....

Quote:
Originally Posted by lukesforester View Post
Hey i just got my forester, I've heard there 10:1 compression ratio.
To me that seems high so would i get better mpg and or better performance from higher octane gas, 89,91 or even ultra94... i work at sunoco lol
That is what's specified, and going to a higher octane will give you zilch in terms of a performance improvement.

There are *some* cars that will tune for the range between 87 and 91 or 93 octane--my son's '97 BMW 318ti (four cylinder) recommends premium but is completely OK to run on regular or midgrade. I believe that the 6-cylinder Outback is the same--recommends premium, but will run on regular with slightly decreased performance.

But if a car is designed for regular, it's fine on regular. I believe my wife's '07 Honda Civic has a 10.5:1 compression ratio, and regular fuel is all that's required.

If you work at a Sunoco and get gas for free, or if you don't have to pay any more for higher octane, you could run it on 89 or something like that, but you really don't need to.

George
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Old 05-11-2008, 07:41 PM   #5 (permalink)
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Quote:
Originally Posted by satalac View Post
use the recommended octane for the car that subaru says. i believe it's 87. please someone correct me if i'm wrong. anything else and you're just wasting money.
For NA foresters I believe the minimum octane rating is 87. I use 93 in my FXT.
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Old 05-11-2008, 08:00 PM   #6 (permalink)
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Quote:
Originally Posted by satalac View Post
use the recommended octane for the car that subaru says. i believe it's 87. please someone correct me if i'm wrong. anything else and you're just wasting money.
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Old 05-11-2008, 09:24 PM   #7 (permalink)
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Originally Posted by wakeabyss View Post
For NA foresters I believe the minimum octane rating is 87. I use 93 in my FXT.
i use 93 in my fxt as well. i don't get the minimum 91 down here. darn .
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Old 05-11-2008, 09:51 PM   #8 (permalink)
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If you're putting 91 in your car thats asking for 87, you might as well just paypal me the extra cash you got there.
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Old 05-11-2008, 11:28 PM   #9 (permalink)
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Default New 09 FXT

I asked the dealer about the Octane after reading the forums here. I read that up until the 09, that anything but premium would overheat the engines on 06-08 FXT's, but after talking to the dealer, he said that my 09 FXT recommends premium with a minimum of 91, but that if I ran 87 that I would do no damage to the engine, but would loose about 4 to 6 HP. He said that the XT's are tuned to premium. I use 91 in Arkasnas and it only about 20 cents more per gallon. Anybody use Octane Booster in thier new 08/09's? I have heard to stay away from them, but if anybody knows of one that works or is ok to use on a FXT let us know. Thanks
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Old 05-12-2008, 03:55 AM   #10 (permalink)
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I have a N/A 04 5 Speed. On my many travels I logged mileage as well as other services. Since day 1, when I run the recommended 87, I get some octane knock. When I run my OBDII display on the passenger seat right next to me, I see the timing retard when I hear that knock. It goes from 42 BTC to 12 BTC ( at least I know the knock sensor is working ). The best mileage I got from 87 was 30 mpg.

Then on a lark, I tried 'plus' 89 ( .10 more per gallon ) , no more knock and no more retarded timing. My mileage increased and on the highway I consistently get over 30 mpg usually in the 33-34 mpg.

For me, and extra $1 or so at fillup is worth the extra 30 or more miles I get out of a tank of gas, and cheaper.

End of my $.02 and experiences.
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Old 05-12-2008, 04:34 AM   #11 (permalink)
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There is a lot of posts already on here if you search for "recommended fuel for turbo" or something like that. This seems to always be creeping back in. LOL

Well, just to sum it up, if you have a Subaru with a turbo, it is critical that you use nothing less than 91 octane. If you run for extended periods of time on regular, you will eventually burn up your turbo for starters, which wouldn't be covered under warranty. I don't know why your dealer told you it was just fine to run regular if premium is recommended. Obviously he didn't get the memo! LOL

If you look in your manual, it also says that in an emergency, you can use the regular gas if premium cannot be found. If you do use regular gas, you will be taking a severe hit on performance (and not just HP will be affected!!!) as the knock sensors will pick up on this and have the ECM (Engine Control Module) to adjust the timing to accommodate the lesser fuel.

If your car specifies regular 87 octane, than it will not run any better or get better gas mileage and you will be wasting your money; It will only run hotter. The ECM cannot adjust for this scenario as it was only tuned to run on the regular 87 gas. I have seen some stations in New Mexico, Arizona, and Nevada that sell regular 85 octane and mid grade 87. Just make sure that you are always using the fuel the car manufacture recommends.

EDIT: Octane Boost WILL NOT improve the quality of fuel. It is not a magic wand to fix everything. As an additional not to that, for the cost of premium fuel vs. regular fuel in the tank, the cost to put in the premium would be cheeper than buying the bottle of boost to put in after the fact!
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Old 05-12-2008, 06:29 AM   #12 (permalink)
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Quote:
Originally Posted by YoGeorge View Post
If you work at a Sunoco and get gas for free, or if you don't have to pay any more for higher octane, you could run it on 89 or something like that, but you really don't need to.

George
LOL I wish
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Old 05-12-2008, 06:48 AM   #13 (permalink)
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Yea, I wouldn't recommend 99% of octane boosters. The majority of them only bump the fuel up a few octane -points-, not even one full octane.
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Old 05-12-2008, 11:28 AM   #14 (permalink)
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Here in Colorado, we have 85/87/91. I use 85 for our Subaru, 87 for our Honda CRX. Compression ratio dictates for that. Our El Camino uses 91.
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Old 05-12-2008, 12:10 PM   #15 (permalink)
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Quote:
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Here in Colorado, we have 85/87/91. I use 85 for our Subaru, 87 for our Honda CRX. Compression ratio dictates for that. Our El Camino uses 91.
well i doubt you bought your el camino for it's great gas mileage .
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