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Yes, while all of you are talking about adding octane with products like Torco, I am wondering what happens if you run a stock STi with regular unleaded in it. I may sound like a real a$$ to the rest of you for asking, but I swear I am asking for someone else.I am overseas in the Army and can't think of anything better to blow 30+ grand on than a STi when I come home in February, but in exchange for him paying the insurance and driving the car while I am deployed, my father the miser wants to run regular unleaded in the car. The sales lady told him he could and I've heard it's horrible. What will happen? Will the knock sensors take over and save the car while robbing power or will it seriously mess up the engine? I have also asked SOA but have not recieved a reply yet.
 

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Wouldn't advise it. Although the ECU will pull timing in association with the knock sensor, the boxer platform is notoriously noisy inside the cylinders. This results in a blanket effect where the knock sensor isn't very active. Using regular gas will most likely ALWAYS result in knock, of which some of it won't be detected. Over time, this knock, or actually pre/post detonation of vapors, will scar your pistons and cylinder walls, resulting in failure. The knock sensor should not be relied upon to allow you to run regular gas. Besides which, your warranty would be voided if the dealer finds out. I've seen evidence of severe knocking in an engine before, and it is not pretty.

If you must run regular, I would get it documented from the dealer lady you spoke with that it is OK and that your warranty will not be impacted. In fact, I would get it from her manager, and the regional SOA rep too, as salespeople come and go, so she could be gone when/if you run into problems.
 

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My dad's the same way. My brother left his Merc 190 16V with my dad when he went to Korea. To make sure he used the premium only that the car requires, he set aside a credit card that he pays to cover the gas, just so our dad wouldn't have any excuses. He also uses it to cover oil changes and maintenance (it is a MB, so maintenance seems like a weekly thing. JK). So far it has kept everyone happy. Now we just need to break him of the habit of passing station after station to find the cheapest price.
 

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Thanks YB and VVVV! Here is what SOA sent me;

Thank you for visiting the Subaru Web site and for your interest in Subaru products! We appreciate you taking the time to contact us.

The 2.5 liter turbo engine is designed to operate using premium unleaded gasoline with an octane rating of 91 AKI or higher. If premium unleaded gasoline is not available, regular unleaded gasoline with an octane rating of 87 AKI or higher may be temporarily used. For optimum engine performance and driveability, it is recommended that you use premium grade unleaded gasoline.

While some owners have opted not to heed this recommendation and may not be experiencing any difficulty, our position remains that premium unleaded gasoline is recommended for this vehicle.

I hope this information is helpful to you, but should you have further questions, please let me know and I'll do my best to assist you further.

Best Wishes,

Natalie Cox
Subaru of America, Inc.
Customer Dealer Services
E-Contact Group
 

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The extra 10 cents on the gallon is not worth having the ECU have to correct itself...91 octane or better, here in Louisiana I have 94...Always put in the best gas on an STi, it's going to cost you a lot more in the long run than if you would have followed the manual, which I am sure clearly states 91+ octane premium gas.
 

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I wouldnt mess around with putting cheap gas in. I've recognized that I bought a nice, expensive, & high performance car and that nothing is cheap for it. Im sure people in Cali or other high gas price states are upset though
 

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What I don't get is that it only costs $2-3 per tank more to get premium. Is it worth that little savings to potentially destroy your engine? Not to me.
 

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Premium gas 92 octane in oregon about 3 mos ago was 2.60 a gallon. With the STi's poor gas mileage it wasn't fun. 15$ would give you a 1/4 tank. Saw an SUV fill up on premium. He handed the gas attendant a 100$ bill and said 'fill it or stop at 100 whichever comes first' The guy put 99$ worth of gas in it!!!!!!!!
 

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I tried to fill my subie's tank up yesterday, and the guy inside the gas station screwed up and had my pump set on regular low octane fuel. Now my subies running like **** and its got me worried. It seems like its misfiring, sputtering and what not. I already put some octane booster in the tank but if anyone has any advice, let me know.
 

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I tried to fill my subie's tank up yesterday, and the guy inside the gas station screwed up and had my pump set on regular low octane fuel. Now my subies running like **** and its got me worried. It seems like its misfiring, sputtering and what not. I already put some octane booster in the tank but if anyone has any advice, let me know.
You're not actually driving in boost are you?
 

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not really! you can drive to redline and never hit boost. its how hard you press on the throttle.


Yea, it's easy to redline the car without hitting boost. In normal every day driving I never hit boost. Boost is the point at which your turbo begins forcing air into the engine rather than the engine just sucking air in on its own.
 

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recommended vs. required

my advise is to check the sticker on the fuel door. typically, car manufacturers will put a label on the inside of the fuel filler area that will either say "premium fuel is recommended..." or "premium fuel is required...".

the engineers who tune the ecu's will have a fuel map and ignition timing for lower octane if the label reads "recommended" vs. "required" the engine will run like crap. on cars that say "recommended" and you use the lower octane, you will typically experience reduced performance.
 

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Octane

How about at high altitude.... 5000 feet and up... using midgrade 89 octane...been doing that and it runs very well.
Owned two years and we have put 25K on it 06 WRX-TR.
I can't reach max boost anyway..up here. Thnx for any input.
All stock except for a 2 1/2 inch ID free flowing muffler.
 

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How about at high altitude.... 5000 feet and up... using midgrade 89 octane...been doing that and it runs very well.
Owned two years and we have put 25K on it 06 WRX-TR.
I can't reach max boost anyway..up here. Thnx for any input.
All stock except for a 2 1/2 inch ID free flowing muffler.
It says on the fuel filler lid "Use only premium gas". I cant believe your being that cheap as to not even use the better fuel. I know honda civic owners who only use higher octane.. on a wrx its required Id think. Your car prolly hates you.
 

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It says on the fuel filler lid "Use only premium gas". I cant believe your being that cheap as to not even use the better fuel. I know honda civic owners who only use higher octane.. on a wrx its required Id think. Your car prolly hates you.
Well, at higher altitude you engine has less compression due to thinner air. Whether or no 89 is acceptable in his case, I *believe* it might be, but I can't say 100%.
 
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