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Old 08-11-2013, 12:17 PM   #28 (permalink)
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Join Date: May 2012
Location: Illinois
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Second time's the charm - '04 Honda Accord EX
90 day: 24.26 mpg (US)

Tengu - '11 Mazda Mazdaspeed 3 sport
90 day: 19.73 mpg (US)
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Originally Posted by Lbar View Post
Throwing mid grade in the mix now?

As far as 87, I don't think, I know. Subaru doesn't have any provision in the tune to handle low octane. Nor should they on a turbo charged engine. Forced induction, timing tables meant for high test, and low octane equals detonation, and possibly a blown motor. Detonation damages everything from the top of the piston on down, ending at the bearings. It would make sense to you if you had a better understanding of engine management and tuning. Take it from someone who does, or better yet do a search.

Some performance vehicles can run either 87 or 91/93 based on a versatile factory tune that will switch but those are reactive systems and not ideal. The OP could pay for a Cobb Accessport and find a Subaru shop that would try to do a custom 87 octane tune. It would cost him over $1000. He would void his warranty, lose power, drive-ability, and probably MPG.

The STi is designed to run on 91. Going to 89 probably wouldn't induce part throttle detonation, but I'm not sure. Light detonation would not be heard while driving so you might have a problem you aren't aware of. 89 would in my opinion cause some detonation under wide open throttle. With the minimal cost savings for the gas it would be better not to risk it if you ever plan to push the pedal down.

My CTS-V is naturally aspirated and it can't function with 87 in the tank. Even with the knock sensors pulling timing the amount of detonation at part throttle is scary. I have a separate custom tune for 87 but I have to load it onto the ecu before filling up because the car can't be driven without detonating. I don't use it though, the car is somewhat lethargic in comparison to the normal tune and the mpg loss negated the fuel cost savings.
It seems like what you said is mostly true, specific to the sti, I can understand that the car is performance oriented but it seems like it would be good practice to throw in the knock sensors just for back up.

I could not find anything for 2013 sti but it seems like for the 07/08 ish models they didn't have the ability to retard timing for regular octane. Which I thought was weird, and was kind of what I was going off of from the beginning. I thought surely the newest one would have the ability to retard timing enough.

Okay finally found something, apparently in the manual it says it can run on 87 temporarily for emergencies, however it's for a 2010 wrx. I can't tell if the warning beforehand says it doesn't apply to the sti. That's what it looks like, though. Does it cost a lot of money to add knock sensing capabilities to the computer? Is it like entirely a thrown out idea because it's the sti version?

Now for an aside about the cts-V, how is rearward visibility? People always complain about how weird the back looks does it make a difference? I like the design of the rear, although, it does kind of make the car look stout. Which kind of goes with the trying to be muscle-y.
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