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Old 01-28-2008, 09:03 PM   #1
Scooby Newbie
Member#: 169433
Join Date: Jan 2008
Chapter/Region: South East
Location: jacksonville nc
2010 wrx
rally blue

Default octane

as long as im posting threads that are ignorant. well i usually put in 93 octane here in hawaii. but what would really be the difference if i just put in 89. the owners manual says to put 93/92. but seriously, obviously the higher octane the better the combustion right? but i kinda want better gas milage since 93 is like 3.50 a gallon on a good day. any ways to optimize gas and performance at the same time.
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Old 01-28-2008, 09:12 PM   #2
Scooby Newbie
Member#: 133283
Join Date: Nov 2006
Chapter/Region: NWIC
Location: Everett WA
2006 WRX TR


I might be wrong but I think it's a waste of money to put 93 oct in your RS. I had a near stock RS for 5 years and always used 87-89 with no problems.
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Old 01-28-2008, 10:40 PM   #3
Scooby Guru
Member#: 71092
Join Date: Sep 2004
Chapter/Region: MWSOC
Location: Delaware County, Ohio
2005 2.5RS Wagon
Regal Blue Pearl


The owner's manual should say to put in 87 if you've got a 2.5RS like your profile says.

Higher octane gas provides NOTHING but greater resistance to knock. If you're not knocking and the ECU doesn't have the authority to advance timing, then you get NOTHING from running higher octane gas. It just costs more.
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Old 01-28-2008, 10:54 PM   #4
Scooby Specialist
Member#: 145883
Join Date: Apr 2007
Chapter/Region: SCIC
Location: Southern California
2008 wrx


i never put 91 in my rs
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Old 01-28-2008, 11:32 PM   #5
Scooby Specialist
Member#: 74907
Join Date: Nov 2004
Chapter/Region: NWIC
Location: salem, OR
98 cam'd EJ251
Wrx Tranny,slowr than ish


Waste of money unless you have higher compression, turbo, or mods that warrant using higher octane. You might ping a little more on steep hills, but generally it's not worth it.

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Old 01-29-2008, 12:15 AM   #6
Scooby Newbie
Member#: 167703
Join Date: Dec 2007
Chapter/Region: MWSOC
Location: MN
2005 '05 2.5RS 5MT
'10 Forester X Limited



Includes a good piece on tuning and how my power comes about from tuning and high compression. Williaty hit it on the head. Higher octane = more resistance to knock = potential for increasing compression/timing. If your '04 RS is stock you'll see very little (if any) tangible gains from anything above 87. Also, premium fuels contain the SAME amount of additives as 87 and haven't be shown to decrease carbon deposits or increase the longevity of the engine.
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Old 01-29-2008, 01:34 AM   #7
Scooby Guru
Member#: 115154
Join Date: May 2006
Chapter/Region: MWSOC
Location: NYC
2005 Outback XT
White on grey


Does it really say Premium in your owner's manual?
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