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We have a 2005 turbo (just got it about 6 weeks ago) that we love! My question is: Does anyone regularly use lower octane gas and what are the issues? Lower mpg? Any engine problems? Poor performance? I filled the tank this AM and considered using regular unleaded, but felt guilty so I went with high test 93 octane. With gas up $0.20 since last week I would like to use lower cost fuel at least once in a while. All comments appreciated, thanks.

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We have a 2005 turbo (just got it about 6 weeks ago) that we love! My question is: Does anyone regularly use lower octane gas and what are the issues? Lower mpg? Any engine problems? Poor performance? I filled the tank this AM and considered using regular unleaded, but felt guilty so I went with high test 93 octane. With gas up $0.20 since last week I would like to use lower cost fuel at least once in a while. All comments appreciated, thanks.

 

You need to run high octane, 91 or greater. The issue is with detonation on high cylinder pressure/compression engines (Turbos) leading to piston damage at higher RPMs. See http://www.prime-mover.org/Engines/GArticles/octane.html

Subaru *requires* higher octane in these vehicles. Use lower octane only in an emergency and/or when higher octane is not available.

 

My area where I live there are a few stations that sell various octanes all at the same price (priced at what other stations are sell 87 for), and one is at least within a resonable driving distance to make it worth while. Check around.

 

I use the Twin Cities Gas Price list for current pricing in this area:

 

http://www.twincitiesgasprices.com/index.aspx?s=Y&fuel=A&tme_limit=4

 

Here's Gas Prices for Vermont (there may be others...)

 

http://www.vermontgasprices.com/

 

 

 

Congrats and enjoy your new ride...!

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My Forester Turbo manual says minimum RON 95. HOWEVER, we measure octane on a different scale over here.

 

We basically have three available at the pumps: 92, 95, and 98 - Germans also have 100 for the FSi engines.

 

SO, don't try to save pennies on the lowest octane fuel and then lose dollars on a blown engine.

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My Forester Turbo manual says minimum RON 95. HOWEVER, we measure octane on a different scale over here.

 

We basically have three available at the pumps: 92, 95, and 98 - Germans also have 100 for the FSi engines.

 

SO, don't try to save pennies on the lowest octane fuel and then lose dollars on a blown engine.

 

I was under the impression however that due to electronically controlled timing on modern engines, the engine will retard timing to account for the lower octane level. My father has a 99 Buick regal GS supercharged, and using 87 octane simply reduces peak horsepower due to slightly retarded timing. Maybe this is only ok for occasional use though.

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In theory, but the high pressure in the combustion chamber - due to turbocharging - could lead to expensive pre-ignition.

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In theory, but the high pressure in the combustion chamber - due to turbocharging - could lead to expensive pre-ignition.

 

The question I have is if there is more danger of damage on a lower octane fuel at higher RPMs than lower, due to the turbo spooling faster?

 

To some degree, is this not true for normal aspirated engines as well (just normal high RPMs)?

 

I would think if you needed to put lower octane in the tank that you should be relatively safe if you don't floor it...

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Yes. If for some reason you are forced to put in a "too low" octane, then staying below 4000rpm and avoiding full throttle would lower the risk a great deal.

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