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Old 10-03-2012, 11:52 AM   #51
Scooby Newbie
Member#: 213303
Join Date: Jun 2009
Chapter/Region: NWIC
Location: Portland, OR
2009 Impreza 2.5i


Higher octane fuel is, in short, just more resistant to knock. Having great knock resistance allows for more advanced timing, creating more power. That's the best I can explain without writing an entire chapter of text. Subaru's EMS will advance timing, if only a little, to accommodate higher octane fuel. Typically the difference is negligible at best, unless you get tuned for the higher octane.
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