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Old 06-12-2013, 08:35 AM   #1
last lemming alive
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Default MPG just seemed to jump - is something amiss

I have a 2011 STI and I've been running Cobb OTS Stage 2 with their down pipe for a while. I've been getting 14-15 mpg when I check it at a every fill up.

Today when I went to fill up I checked it and it said 20.1 mpg. I haven't changed my driving style that I'm aware of - maybe no gunning it so much, but not that much different than normal. After I filled up I drove to work - gunned it a bit every now an then - and it came back 19.1 mpg. Again, never had that before.

It is hotter now down here - in the low 90's, but I've never had this kind of jump in MPG in any of the 3 Subaru's that I've owned. I'm going to do a log on the AP and see what I get, and I'm going to check if I'm hitting boost.

Overall the car seems to run normal though my butt dyno seems to tell me I'm a little light on power, but the temps have been in the 90's, so I'm not sure that wouldn't be the cause there.

Assuming this isn't just a fluke, what are some things I should be looking at or concerned with? My turbo?
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Old 06-12-2013, 09:37 AM   #2
the suicidal eggroll
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I think your real concern should be the 14-15 mpg you used to be getting. 19-20 is normal, 14-15 is about the worst I've ever heard of on stage 2.
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Old 06-12-2013, 09:49 AM   #3
last lemming alive
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well, 14-15 is what I've always got on my subarus. I'm in stop and go traffic from work to home for all 7 miles. So for me its always been quite normal.
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Old 06-12-2013, 09:53 AM   #4
the suicidal eggroll
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You can log your DAM, knock correction, and fuel trims. Better mileage is rarely an indication of a problem though, especially since you're not really feeling a power difference.
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Old 06-12-2013, 02:01 PM   #5
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Maybe the change from winter/summer blend fuel? Even though its pretty late in the year. Did you change your intake filter?
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Old 06-12-2013, 03:57 PM   #6
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Get tuned for e85 and watch ur mpgs really fall off lol
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Old 06-13-2013, 12:56 PM   #7
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I wonder how accurate the AP reading really is. Are you reading the MPG from the AP or actually dividing milage/gallons?
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Old 06-13-2013, 02:35 PM   #8
last lemming alive
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I'm reading the mpg from the car dash. So it should be consistent.
Regardless last night i did some peak boot runs and was consistently hitting 18.1. Except for one run where I hit 19.6! Never seen that before and not sure why it spiked on that run. I am running a dp + stock cat back.
Also the mpg was back in the 14's so I guess everything is normal. I'll just keep an eye out on it. Summertime hp sucks down hear. It's 94 degrees + 90 % humidity. Add to that a full tank and the A/C being on and I'm pretty sure I know why I felt I was down a little bit on hp.
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Old 06-13-2013, 04:00 PM   #9
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14mpg is still pretty low!

Hm, odd that it went up then after you smashed it it went back down...

-Mark
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Old 06-13-2013, 05:34 PM   #10
last lemming alive
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14 was great compared to the 11 I got on average with my RX8
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Old 06-13-2013, 05:58 PM   #11
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Quote:
Originally Posted by last lemming alive View Post
14 was great compared to the 11 I got on average with my RX8
Ahhh, the old RENESIS! I love those bubbly little motors! So much potential for reliability. I used to ONLY track mine with a straight pipe, Intake and Tune...the car STILL gets tracked by my buddy. Power expectations can't be set high but hey, we just wanted balance.

In all honesty, even with stop and go I think your average can be a bit higher, out here we've had a few clients acknowledge over 25 on the highway so I'd fathom you can get a bit more out of it.

Have you had any preliminary inspections performed? Smoke test to ensure no leaks are present or what not?

-Mark
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Old 06-13-2013, 07:40 PM   #12
last lemming alive
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No tests. But to visualize my situation I drive a 1/4 mile out the the parking garage then I'm in bumper to bumper traffic (think traffic jam) for 6 miles till the last 1/8 mile to my house. Honestly this is the same mpg I got on my 06 wrx, my 09 wrx and now my 11 sti. It's usually between 14-16 mph. Usually nearer 15 mph. In fact every car I've had gets about 6-8 mph lower than advertised for city driving. I get a out 21-22 mph on the highway. So since my bad gas milage has happened to all of my different cars from different makes I've just learned to deal with it. The Cobb OTS runs really rich too so that's not helping. And all my subys have been stage 2 with Cobb OTS maps.

Last edited by last lemming alive; 06-13-2013 at 07:45 PM.
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Old 06-13-2013, 07:44 PM   #13
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Yeah the rx8 is one of the best handling cars if not the best handling car I've ever driven. Well maybe not as good as the 2006 Porsche gt3, but I wasn't able to throw that one around so much.
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Old 06-13-2013, 08:17 PM   #14
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Quote:
Originally Posted by last lemming alive View Post
The Cobb OTS runs really rich too so that's not helping.
If the traffic really is like you said, you'll be idling or cruising most of the time, which means you're going to be at stoich with any tune. The "richness" of the tune is only at WOT, which you'll almost never be hitting with traffic like that.
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Old 06-13-2013, 08:35 PM   #15
last lemming alive
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Well all I can tell you is I'm constantly stopping and going and I've had bad gas on every car I've ever owned (that's about 7) since living where I live so either I have had 7 new cars in a row with something wrong or traffic is the cause.
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Old 06-13-2013, 08:47 PM   #16
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Idling and cruising at 5 mph will definitely kill mileage, I was just saying that the Cobb OTS tune being "rich" doesn't have anything to do with it, since all tunes are going to idle and cruise at stoich.
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Old 06-13-2013, 09:06 PM   #17
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Quote:
Originally Posted by last lemming alive View Post
No tests. But to visualize my situation I drive a 1/4 mile out the the parking garage then I'm in bumper to bumper traffic (think traffic jam) for 6 miles till the last 1/8 mile to my house.
This sounds like hell

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Old 06-13-2013, 09:43 PM   #18
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sounds like you have been using the wrong fuel

I know I get 3-4mpg better with good fuel vs bad fuel
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Old 06-14-2013, 08:57 AM   #19
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Your IAM seems to be happy with the fuel you are using and the way you are driving. Continue for similar results.
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Old 06-14-2013, 09:35 AM   #20
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I'm getting 22.5mpg every tank on stage 2.
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Old 06-14-2013, 04:10 PM   #21
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Quote:
Originally Posted by Uncle Scotty View Post
sounds like you have been using the wrong fuel

I know I get 3-4mpg better with good fuel vs bad fuel
I've always used Chevron 93, and I'm tuned to 91 stage 2. Is there something in that maybe?
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Old 06-14-2013, 04:14 PM   #22
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Quote:
Originally Posted by MtnXfreeride View Post
This sounds like hell
It aint no picknick!
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Old 06-14-2013, 04:17 PM   #23
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Quote:
Originally Posted by the suicidal eggroll View Post
Idling and cruising at 5 mph will definitely kill mileage, I was just saying that the Cobb OTS tune being "rich" doesn't have anything to do with it, since all tunes are going to idle and cruise at stoich.
Oh I have no doubt you're right about this, It might just be my driving style that's contributing to it. Though I've driven manuals for 25+ years and until I moved where I do now, I've never had "bad" gas mileage that I do now - that's why I contribute it to the traffic - and the fact that its been the same for the last 5 or 6 cars I've own while living here.
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