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What Octane number do you use inyour gas tank?

  • 91-93, Yea Baby!!

    Votes: 112 36.7%
  • 89, does the job, no complaints.

    Votes: 64 21.0%
  • 87, I'm poor, only wish i could use the high stuff.

    Votes: 129 42.3%

  • Total voters
    305
161 - 180 of 195 Posts

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Registered
2000 2.5 RS Matte Red
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167 Posts
87 89, car runs good with the cheap stuff. Every once and a while I run some techron or seafoam through it.
 

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Registered
Subaru
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321 Posts
I run 93, but then again it's only $2.60/gal for 93 here. It's been under $3 for the last two months. :D

There's no e-free stations nearby or I'd run that. The closest is about 40 miles away.
 

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Baby❤Daddy
98L Wagon
Joined
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27,848 Posts
yes.


iirc... even the 10% ethanol regular 87 saps about 20% of your MPG. i was tracking mine pre turbo, and i was getting about 21-22 on the 10% regular, and if i drove like a sane person, i could 25-26 on e-free.
 

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Registered
2005 Baja Turbo
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1,448 Posts
I alternate between 92 E10, 93 ethanol free, and in the summer I run E10 with an octane booster, or straight up 100 lead free for the track.

On straight 93 octane, it knocks like mad during the summer. Octane booster is enough to stop it. During the winter, it's fine on 92 or 93 octane. If I'm racing, I drop in straight 100 lead free just to be safe... Last time, I mixed 10 gallons of 100 with 5 gallons of 93 E0, and it did pretty good.
 

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Registered
1997 Impreza Brighton
Joined
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491 Posts
iirc... even the 10% ethanol regular 87 saps about 20% of your MPG. i was tracking mine pre turbo, and i was getting about 21-22 on the 10% regular, and if i drove like a sane person, i could 25-26 on e-free.
That's odd. A 20% loss in MPG from 10% ethanol would imply that the ethanol is not only not combusting, but requiring an extra 10% of the heat produced from the gas just to evaporate.
I wouldn't expect 10% water in gasoline to cause a 20% loss in MPG (if it was somehow evenly mixed).
I'm extremely skeptical, but it makes me tempted to try it in my DD and see what happens.

Or are you comparing driving crazy on normal fuel and getting 21-22 MPG to driving sane on ethanol-free and getting 25-26 MPG?
 

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Registered
1997 Impreza Brighton
Joined
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491 Posts
what i meant by that...driving sane i can get upwards of 25-26 on e-free. driving the same on both..it's about 23-24 mpg on e-free.
Okay, those numbers make a lot more sense (though still a bigger difference than I'd expect).

I think I found an E-free station near my work. I'm going to have to try it in the commuter car.
 

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Registered
'04 PSM WRX Premium
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8,339 Posts
Holy bumps from the dead.

For what it's worth, when I had my '98 2.2 and did a VERY consistent commute each day without traffic on the highway to college back and forth, I logged every fillup.

Final conclusion was 89 gave better gas mileage than 87, which was exactly equal to the extra paid for it. For that extra 10 cents, you got .1 divided by gas price % better gas mileage. The car did run better, but again, no documentation of that besides my butt dyno. It was noticeable.

Never tested 93, but my gut was it wouldn't out weight the extra 30 cents more. Car probably would have ran slightly even better.

By better, I do not mean noticeably more power, but rather smoother, less 'pinging', and quieter operation.

I'd recommend everyone run 89 if possible in your state. 91 may also be a good choice. 93 and up, on the stock ECU and tune probably isn't worth it, or any race gas.
 

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Experimenter
Tubaru Pickup
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3,913 Posts
in my old 300m, i used 93 and the extra mileage washed the cost. but the 93 bumped my long term timing maps up and anytime id put 87 in it, the car would run terrible the next 100 miles until it relearned. running higher octane gas will let your car advance timing further and pick up some performance and mileage to an extent. most people argue this because they think the results are instant, they arent, the ecu takes time to readjust its maps.
 
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