Yes I'm aware the manual says put 93 octane only....and i do....i was presented with the question of why.......and that it "doesn't matter" if i put 91 or 89 in it.......i really didn't have an answer other than what the manual says to do.......I assume the reason is because the car is tuned to 93 and anything else can "gum " up the engine???? ( sorry the search function wasn't very helpful in this matter ) why exactly must we put in 93......what can happen if you dont?

 

Anything less may cause the engine to detonate, which will cause the ECU to pull timing to prevent further detonation which will decrease power and potentially damage the motor.

 

93? Its recommended on the WRX. Then required on the STI, but can use 91 until you find 93. I remember its something like that

 

Using the Search feature, here is a recent thread that sums it up in a general way.

Octane requirement is dictated by several factors like engine tuning (either from the factory or aftermarket), static compression ratio, turbo boost settings, etc. Engines under boost require higher octane since cylinder pressure under boost is similar to a normally aspirated engine with very high static compression ratio - more air and fuel is forced into the cylinder under boost than would normally be the case in a low compression engine without a turbo.

Do NOT try to run a WRX or STi with a lesser fuel than the minimum factory requirement thinking that you can save money. You risk engine damage, you void the factory warranty, and the engine will run pig rich to try to protect itself from detonation. It will also not be fun to drive in this mode.

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"…axles of evil…" - george w. bush

 

thanks guys.

 

You can use anything from 91-93 octane on the WRX and STi/STI unless you're tuned for 93 octane.