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Discussion Starter #1
:rolleyes:

I was wondering what octane rating most people ran in their RS's? I didn't know if anyone has noticed much of a difference in their performance or what was best. I am a new subie junkie and just thought I would get some useful info from someone who has ran their car on different octane level gases.
 

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1999 2.5 RS Silver
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333 Posts
the stock rs ECU is tuned for 87 octane. Higher will work, but it won't really improve performance
 

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Two Mini Coopers!
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I'll second that motion. Higher octane is generally only used for knock control, which tends to be a problem with turbocharged cars. No turbo means you can just use the cheap stuff.
 

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hmmm...that's strange. cause i have notice on getting bad gas mileage on 87 and 91. but on 89, i had the miles per gallon pretty good. and btw, i do a lot of city driving.
 

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I was gonna post about this, too. I have a ProECM chip on my car, and was using 93 octane for a bit. I thought about it and decided to use 90 just to see what happpens. I am not hearing any knocking sounds and my power has gone up a bit. I think this is strange. Is winter fuel any different from summer fuel?
 

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I use 87. That is the minimum recommended by Subaru. all Octane means is the amount of resistance to burn of the gasoline. This is why turboed cars or cars with really hight CR need to use higher octane gas. The air-fuel mixture is being compressed more and PV=nrT, which means that when something is compressed, it gets hotter. if the gasoline ignites itself, it can be very damaging on the engine. this is called knock. you won't hear it in a modern car. the knock sensors are sensitive enough that they will pick it up while it is still minimal and retard the timing to prevent it. of course, this means less power. anyway, back to the topic at hand. if you plan on using a higher octane of fuel, reset your ECU or you will probably get a decrease in performance. the Subaru ECU is very adaptable and once it gets set on a certain octane, switching to something else will fuck with its head. FWIW, I get shit for mileage in the city, but it does well on the highway. i also get better mileage on pure gasoline then the 10% methonal crap the EPA forces on us in most major metropolitan areas.
 

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1999 2.5 RS Silver
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10th Warrior said:
I use 87. That is the minimum recommended by Subaru. all Octane means is the amount of resistance to burn of the gasoline. This is why turboed cars or cars with really hight CR need to use higher octane gas. The air-fuel mixture is being compressed more and PV=nrT, which means that when something is compressed, it gets hotter. if the gasoline ignites itself, it can be very damaging on the engine. this is called knock. you won't hear it in a modern car. the knock sensors are sensitive enough that they will pick it up while it is still minimal and retard the timing to prevent it. of course, this means less power. anyway, back to the topic at hand. if you plan on using a higher octane of fuel, reset your ECU or you will probably get a decrease in performance. the Subaru ECU is very adaptable and once it gets set on a certain octane, switching to something else will fuck with its head. FWIW, I get shit for mileage in the city, but it does well on the highway. i also get better mileage on pure gasoline then the 10% methonal crap the EPA forces on us in most major metropolitan areas.
^
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That guy=smart:eek:
 

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95 Impreza L AWD
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I use 93 octane primarily, but I have a turbo. Sometimes I'll get 92 if I'm feeling lazy or 94 if I feel like spending money. Right now it doesn't matter, since I'm ALWAYS running rich and often get popping from the exhaut; sometimes it sounds like gunshots! Before the turbo, 87 was fine, although a friend of mine only uses 94 on his '98 RS; I think that's all he's used since it was new, and he's just recently gone turbo as well. You may want to try 89 from what others are saying, but I see no need to run premium. :)
 
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