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Discussion Starter · #1 · (Edited)
So this videohttps://www.youtube.com/watch?v=F1JmOKKAgyQ&feature=em-uploademail was posted on the forum in the AEM Intake thread I decided to be a test dummy and remove mine and see if there is a difference. Yesterday was the first drive after removal and my first observations was not a happy one. 1. A loss of power in the low rpm range which is where I generally stay, and it felt like I had to give more throttle than i am use to. I did not reset the ecu and it was snowing yesterday with temps in the low 20's, so im guessing maybe these factors need to be accounted for so as I d0 a little more driving I can give a better insight. One thing I did notice is that after 30 mins of driving my car still did not reach its usual 190-197temp. Usually after about 15 mins of driving I stay there but my car wouldn't break past 183 and if I speed up the temp would actually drop down like 2-5 degrees. Ill keep updating as I go on.
 

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Dang it! I was just about to post my results and I came across yours. Well anyway I did the same thing, I cut mine out as I did not see a need for it, especially with a K&N replacement. It appears my results have fared better though. The throttle seems a bit touchier and more responsive, normal and aggressive acceleration is about the same if not slightly better but not too noticeable. Biggest thing is MPG, city driving is about the same, 1-2 MPG better, highway is the biggest jump, about 4-5, for a mixed improvement of 2-4 MPG. Averaging now 18-19 MPG per tank where i was averaging 16-17 MPG. I'll take what I can get cause I'm still really pissed at the overall MPG performance of this car being that it was advertised much higher. First Disclaimer, I'm in South Florida so my driving temps are way different than yours.

https://www.ascentforums.com/forum/10-engine-technical-discussion/6327-secondary-air-filter.html
My original post asking about it, couple people said to leave it. So far I am liking the results though. I did talk to Subaru Parts to replace it is $40, worth it to try.

** I am not a professional mechanic!! Nor am I telling anyone to cut theirs out, just sharing my experience**
 

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Discussion Starter · #4 ·
Dang it! I was just about to post my results and I came across yours. Well anyway I did the same thing, I cut mine out as I did not see a need for it, especially with a K&N replacement. It appears my results have fared better though. The throttle seems a bit touchier and more responsive, normal and aggressive acceleration is about the same if not slightly better but not too noticeable. Biggest thing is MPG, city driving is about the same, 1-2 MPG better, highway is the biggest jump, about 4-5, for a mixed improvement of 2-4 MPG. Averaging now 18-19 MPG per tank where i was averaging 16-17 MPG. I'll take what I can get cause I'm still really pissed at the overall MPG performance of this car being that it was advertised much higher. First Disclaimer, I'm in South Florida so my driving temps are way different than yours.

https://www.ascentforums.com/forum/10-engine-technical-discussion/6327-secondary-air-filter.html
My original post asking about it, couple people said to leave it. So far I am liking the results though. I did talk to Subaru Parts to replace it is $40, worth it to try.

** I am not a professional mechanic!! Nor am I telling anyone to cut theirs out, just sharing my experience**
Did you reset your ecu(remove negative battery cable) or did you just drive and go. I definitely think there is more air coming the intake and that's why the car was a little confused. Today is almost double the temp from yesterday air fueland I will do a WOT pull and record Mass Air flow rate and AFR just to see if there are any concerns.
 

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No I didn't, it doesnt take long for the computer to learn and adjust accordingly. Right off the bat the acceleration from a stop was a little jumpy but has since smoothed out.
 

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I watched the video and easy decision for me - taking it out!!!

Or I can wait until it hits like 300K mi to remove it at the end of its life (I'm thinking of the charcoal canister as comparison).
 

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Discussion Starter · #9 ·
100 miles without carbon filter and finally the acceleration returned and I was able to really test this out.
Acceleration is pretty much the same but I do notice a slight increase in power 4k to redline.
When going WOT it does sound like there is a little more grunt in engine noise but its nothing that will wow you or annoy you.
Still waiting to see what fuel economy is like but it seems promising.
I'm still running 93 octane and using sport mode 7 for throttle controller
 

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I understand this stuff is fun and you want to try this despite what the conclusion of the video was. I came away from that video deciding not to remove the charcoal filter because the the results were negligible.

"Maybe results are different with a turbo motor" is a valid hypothesis. So the results of testing that would be valuable to this community.

You guys should conduct tests exactly like the video, otherwise any differences that are felt on the butt dyno absolutely cannot be trusted with any degree of confidence.
 

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Discussion Starter · #11 ·
Little update: 140 miles with the charcoal filter removed and I'm really liking it. Its almost like everyday the car feels better with it off. I have not done any real testing on it yet just giving my feedback from everyday driving. Last night I also noticed that you can actually hear the turbo spool now when you give a good amount of throttle. The spool is very faint but its there. Not sure if you need an after-market filter + removal of charcoal filter to hear it but im sure if you removal the intake air duct it will be more noticeable.
I'll try to do some MPG testing and some data logging when I get a chance. I am in contact with the dyno shop to see If I can get a good deal on using a dyno to get some tests done. I really want to see if there is a difference in octane used but I would have to make separate dyno days for that. Ill Keep you guys updated. In the youtube video posted about charcoal filter removal they only discussed peak horsepower but never discussed how it affected the whole powerband which I think is more important.
 

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@DRE18 what mileage are you getting? I live in SoFlo too. I get right at 20MPG every tank.
And btw, my 2015 Forester XT didn't have that other filter in it either, not even when brand new.
I am averaging 18-19 MPG since removal, albeit my commute sucks! about half way thru 3rd tank without it. running on 87. Again slight improvements on throttle response and appears overall power.

As the 15 Forester XT, if you remember the NA Forester as well as every other NA Subaru had the PZEV tag on it, Partial Zero Emissions Vehicle. So I would assume those would have the carbon filter as it is an emissions related device. The XT's and WRX's did not have the badge so I think that is the reason they did not come with the filter. Personally I am satisfied with the results, it seems like an over complicated and efficiency robbing solution to a very small problem. I mean seriously the amount of fuel vapor escaping can't be that much.
 

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I can understand using carbon air filters for the cabin air system, but why would you need to use one for the engine?
 

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I can understand using carbon air filters for the cabin air system, but why would you need to use one for the engine?
It's for emissions: it captures hydrocarbons remaining in the intake system when the engine is stopped. Engineering Explained just did a video on this and the results of taking the filter out (he even did it in a Subaru). Spoiler: there is a negligible difference in power gained from removing the charcoal intake filter.

https://www.youtube.com/watch?v=F1JmOKKAgyQ
 

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I took it off, I have k&n, I can feel more power in high rpm..pull more smoothly....I like how it run now.... if I remember correctly, it is a bit louder.. then before....
 

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The stock filter does a better filtration job than the reusables, especially for fine particulates. Since I off-road, I use stock or stock comparable filters only. And, I keep the carbon filter as a last line of defense.
 
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