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Old 09-03-2010, 02:30 PM   #1
RaineMan
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Default Gasoline for the 2.5?

Hey all.

What grade of gasoline is generally recommended for the naturally aspirated 2.5?

Here in UT we have 3 grades available... 85, 87 and 91. I have generally been one to put the highest grade available in high compression or boosted engines. But is the 2.5 happy on 85 or 87?

Back in NC (where I'm from) we had 87, 89 and 93. So I am really wary about putting 85 in anything.
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Old 09-03-2010, 02:58 PM   #2
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I run 87 octane in mine at this point, many claimed they knock on 87, and my datalogging confirmed this, but I still run 87.
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Old 09-03-2010, 03:27 PM   #3
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Quote:
Originally Posted by RaineMan View Post
Back in NC (where I'm from) we had 87, 89 and 93. So I am really wary about putting 85 in anything.


Whats your elevation? That might explane the 85. 85 at around 5000ft will behave the same as 87 or so around see level because of the air density. Just be aware that if you are running 85 and make a trip down to lower elevation you will have some issues with nock. I would just stick with the 87 to be safe.
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Old 09-03-2010, 03:32 PM   #4
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The altitude in Salt Lake is pretty high. I believe it averages somewhere around 4300ft.

If someone has datalogs showing knock on 87 I'll go back to Premium (91). That was my primary concern. I don't mind paying a few bucks extra when I fill up.
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Old 09-03-2010, 03:32 PM   #5
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For the extra few cents a tank, I would run 87 or 91.

My motor knocks on 87 so I run 93 octane. (91 is not available here)
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Old 09-03-2010, 03:39 PM   #6
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i run whatever premium is available. im not sure that i have a lot of reason to, but its extra insurance for me the way i see it.
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Old 09-03-2010, 03:45 PM   #7
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http://forums.nasioc.com/forums/show...ghlight=octane

I believe this is now a zombie horse...as in it was kicked to death, kicked while dead and has now come back again for some more kicking

Theoretically 87 is OK, anecdotally higher is better.

And don't use 85 - per the manual "The 2.5-liter non-turbo engine is designed
to operate using unleaded gasoline with an octane rating of 87 AKI or higher."
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Old 09-03-2010, 03:48 PM   #8
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Quote:
Originally Posted by Floyd420 View Post
http://forums.nasioc.com/forums/show...ghlight=octane

I believe this is now a zombie horse...as in it was kicked to death, kicked while dead and has now come back again for some more kicking

Theoretically 87 is OK, anecdotally higher is better.

And don't use 85 - per the manual "The 2.5-liter non-turbo engine is designed
to operate using unleaded gasoline with an octane rating of 87 AKI or higher."
Thank you. I figured this had to have been posted somewhere on here before. I'll switch back to premium next time I fill up.

Car didn't come with an owners manual... was a repo so I got the car, one key, one fob, and that's pretty much it.
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Old 09-03-2010, 11:20 PM   #9
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Mine also knocks or pings on 87. I've moved to 89 since it's only 10 cents more and no more pinging. 93 is 40 cents more... that's too much, IMO.
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Old 09-04-2010, 12:15 AM   #10
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Mine runs fine on 87, no knock, nothing, it will knock when I use a low-grade oil.... Maybe it has more to do with that than we think... I use castrol or mobil-1 20/50, when I can't find that, it will knock on base grade fuel..... I've been using 20/50 since I drove a Porsche, all of my cars have ran better with that oil. Obviously I switch to 5/30 in the winter... No knock at mid grade.....and yes it's all synthetic.

Last edited by suex; 09-04-2010 at 12:16 AM. Reason: Spelling
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Old 09-04-2010, 01:37 AM   #11
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I personally use 89. I might fill up with 93 once a month just to clean out the engine.

From what I was told by a truck driver that delivers the gas, he said that on the higher grades there is extra additives that clean out the engine. Not sure if its true or not but I still do it once a month.
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Old 09-04-2010, 07:05 AM   #12
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Has anyone noticed a difference in gas mileage with the different gas grades?
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Old 09-04-2010, 08:21 AM   #13
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Gasoline for the 2.5? short answer, YES!
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Old 09-04-2010, 09:31 AM   #14
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Quote:
Originally Posted by IanB View Post
I run 87 octane in mine at this point, many claimed they knock on 87, and my datalogging confirmed this, but I still run 87.

What software do you use for datalogging?
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Old 09-04-2010, 10:18 AM   #15
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Quote:
Originally Posted by cmiovino View Post
Mine also knocks or pings on 87. I've moved to 89 since it's only 10 cents more and no more pinging. 93 is 40 cents more... that's too much, IMO.
Your EJ22 OBS pings when you put 87 in it? WTF is wrong with the gas in your town?
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Old 09-04-2010, 10:37 AM   #16
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I used 87 for the first 1.5years of owning my impreza and thought there wouldn't be a difference. I listened to what some said and moved over to 93 and noticed it being a bit smoother. now I have a 93 tune so i'll be using it from here out but 87 definitely isn't a huge difference. I just wouldn't go any lower (even with the elevation difference) like a few people stated above.
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Old 09-04-2010, 11:03 AM   #17
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Quote:
Originally Posted by S10Crazzy View Post
What software do you use for datalogging?
ROMRAIDER software with a VAGCOM cable.

Quote:
Originally Posted by dgsblb2 View Post
Your EJ22 OBS pings when you put 87 in it? WTF is wrong with the gas in your town?
Have you datalogged your engine? I wouldn't have guessed I was pinging either, and was a staunch supporter of the "your engine calls for 87, that's all you need" club, but upon datalogging the proof was right there in front of me. Hard to argue with that.
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Old 09-04-2010, 04:02 PM   #18
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Quote:
Originally Posted by bilzer07 View Post
Has anyone noticed a difference in gas mileage with the different gas grades?
Yes, I've hit my highest MPGs with 89 and lowest with 87. $500 worth of gas tested. Yes, there is a difference, IMHO.
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Old 09-10-2010, 07:17 PM   #19
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[quote=IanB;31795162]ROMRAIDER software with a VAGCOM cable.



VAG-COM cable is for a VW/Audi This cable also works with Subaru
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Old 09-10-2010, 08:01 PM   #20
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[quote=S10Crazzy;31853645]
Quote:
Originally Posted by IanB View Post
ROMRAIDER software with a VAGCOM cable.



VAG-COM cable is for a VW/Audi This cable also works with Subaru
It does with some of them!

http://forums.nasioc.com/forums/show....php?t=1914025
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Old 09-12-2010, 09:58 PM   #21
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fwiw, my observations with a stock 07 2.5i was that I saw about a 10-15% increase in mileage when I switched from 87 to 91. The car ran smoother and more responsive with 91.

I observed the mileage from new running on 87, calculating random tanks every now and then, then leading up to the switch, for a few weeks to verify the random sample was accurate... then switched... I followed mileage on 91 for about 6 months. Driving habits regarding route and mileage was a standard routine throughout the entire test on both fuel ratings, so there is a marked change.

Where I am, 91 is only 9-12% more expensive than 87, so you do end up saving money
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Old 09-13-2010, 05:42 PM   #22
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93 oct. on the 2006 2.5i but then again I'm supercharged so I sure don't want to blow my motor....100 oct would be amazing more boost less worries..but you N/A's can run 88 and thats as low as I would go...at least I did when I was N/A lol
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Old 09-13-2010, 05:58 PM   #23
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If you want more octane... go E85.
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Old 09-13-2010, 07:09 PM   #24
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Quote:
Originally Posted by VIsubi View Post
93 oct. on the 2006 2.5i but then again I'm supercharged so I sure don't want to blow my motor....100 oct would be amazing more boost less worries..but you N/A's can run 88 and thats as low as I would go...at least I did when I was N/A lol
You're finally supercharged eh? When did it finally go in? Are you running your own stuff or is it the raptor?
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Old 09-20-2010, 07:54 PM   #25
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Quote:
Originally Posted by Sir-Knight View Post
fwiw, my observations with a stock 07 2.5i was that I saw about a 10-15% increase in mileage when I switched from 87 to 91. The car ran smoother and more responsive with 91.

I observed the mileage from new running on 87, calculating random tanks every now and then, then leading up to the switch, for a few weeks to verify the random sample was accurate... then switched... I followed mileage on 91 for about 6 months. Driving habits regarding route and mileage was a standard routine throughout the entire test on both fuel ratings, so there is a marked change.

Where I am, 91 is only 9-12% more expensive than 87, so you do end up saving money

+1

I did generally the same test. Multiple trips in different temps. When I was using 89, I got better gas mileage than 87. The pinging/knocking went away for the most part too. There is still minor chatter with a cold engine, but once warmed up, it's completely inaudiable.

The price you'd pay for 89 will pay itself back in better gas mileage, therefore you aren't loosing any money by using it. Seems like a win win to me.
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