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Discussion Starter · #1 ·
I didn't succeed in getting it to fit 100% in the box, so I got it in as far as it would go and was able to bolt down two of the screws, but the stock air filter fit fine. I read you can cut the rubber around the neck of the air filter to get it to fit better but I don't know if that's a great idea.

Also, it does sound noticeable louder, but I could swear it's a little less fast now, at least on the low end. And my mpg went down to 27.5 since putting it in. I was at around 29-30 with the stock one. I thought the idea was more mpg, not less so any thoughts on that?
 

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I didn't succeed in getting it to fit 100% in the box, so I got it in as far as it would go and was able to bolt down two of the screws, but the stock air filter fit fine. I read you can cut the rubber around the neck of the air filter to get it to fit better but I don't know if that's a great idea.

Also, it does sound noticeable louder, but I could swear it's a little less fast now, at least on the low end. And my mpg went down to 27.5 since putting it in. I was at around 29-30 with the stock one. I thought the idea was more mpg, not less so any thoughts on that?
I can see the MPG's going down, More air can equal more fuel burning. It also depends on how you drive. Sometimes getting the filter in requires a bit of elbow grease.
 

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Moved to the Duratec TiVCT Performance section.
 

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That Guy
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You shouldn't have to cut it. It is a bit of a pain to install but it should fit just as well as the OEM does to close the lid of the box properly.
 

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Discussion Starter · #5 · (Edited)
Thou shouldn't have to cut it. It is a bit of a pain to install but it should fit just as well as the OEM does to close the lid of the box properly.
But if you hold the K&N one up to the stock one you can see it's longer, so there's no way for a direct fit that I can see. I tried forcing it to go on further, but I couldn't get it to budge. The airbox itself is a really poor design. The screws broke two of the things they screw into. It'd be nice if it were those metal clips like everyone else uses.

Does the cover even need to be on 100% anyway? It's like 99% closed. My understanding is it's basically a cold air intake anyway and those are usually completely uncovered...
 

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I own an early K&N for the MK3 Focus. I bought a new one for the ST. Well the new on IS about 1/8 inch too damn long.
Side by side the later filter of the same model number is about 1/8 too long. I TRIED to install the longer one... PITA, and no way will it fit. It distorts the airbox so much I could no longer get the lid back in properly.You can squeeze it tto fit into the slots in the airbox bottom, and sort of get the lid on, but it will just not screw down fully. I tried several times refitting the filter, no go.
I was able to put in the old K&N filter I had in the SE into the ST no problem.
So somebody screwed up the size of the newer K&N filters and they do not fit.
(unless you did shave off 1/8 inch or so from the rubber end).


I have no idea if K&N is aware of the problem or not.
But I CAN SAY the later, too long filter is impossible to squeeze into the box AND get the box lid on properly. [:(!]

I would think cutting the rubber seal end 1/8 inch would solve the issue. However i did not do that, I just stuck in the other one I owned, even though it had 12K miles on it.
 

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I had both the regular K&N and the open-ended K&N in my Mk3 with the lid closed normally.

In all fairness though, I make my grilled cheese sandwiches with cheese on the outside. I'm capable of some pretty amazing feats.
 

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Can you give us a picture and/or part number to the filter you got?
 

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My K&N fit perfectly too. I thought the same thing, I thought " how the hell is this gonna fit? Its a tad bigger" but after 5 mins i finally got it. You do have to put some elbow grease into it. Its hard and you will feel like your breaking it but your not!
 

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Discussion Starter · #11 ·
My K&N fit perfectly too. I thought the same thing, I thought " how the hell is this gonna fit? Its a tad bigger" but after 5 mins i finally got it. You do have to put some elbow grease into it. Its hard and you will feel like your breaking it but your not!
When I felt like my hand was breaking I stopped pushing. I tried twisting it while I pushed and just pushing. I couldn't get it to go in any further without possibly breaking the whole box.
 

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Discussion Starter · #12 ·
I own an early K&N for the MK3 Focus. I bought a new one for the ST. Well the new on IS about 1/8 inch too damn long.
Side by side the later filter of the same model number is about 1/8 too long. I TRIED to install the longer one... PITA, and no way will it fit. It distorts the airbox so much I could no longer get the lid back in properly.You can squeeze it tto fit into the slots in the airbox bottom, and sort of get the lid on, but it will just not screw down fully. I tried several times refitting the filter, no go.
I was able to put in the old K&N filter I had in the SE into the ST no problem.
So somebody screwed up the size of the newer K&N filters and they do not fit.
(unless you did shave off 1/8 inch or so from the rubber end).


I have no idea if K&N is aware of the problem or not.
But I CAN SAY the later, too long filter is impossible to squeeze into the box AND get the box lid on properly. [:(!]

I would think cutting the rubber seal end 1/8 inch would solve the issue. However i did not do that, I just stuck in the other one I owned, even though it had 12K miles on it.
I want to try that. I read a few people did that and supposedly it worked, although that's an extremely annoying fix after spending $55 on the part. I emailed K&N about it and they ignored me. I'll try trimming it back on the next warm day. It's supposed to be like 5 degrees tomorrow and possibly -5 on Friday (CT), but I hear Sunday's gonna be 40 degrees and rainy. That'd be the perfect day to do it.
 

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I had some trouble installing mine too. It took a while to get it in the right position and to get the whole filter to fit. I would describe the filter as JUST being able to fit properly. Maybe double check that the filter is on the ring all the way? my screws broke the box too =/
 

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wow.. when i installed mine the first time (when I had 2012 Focus), I couldn't get it to fit in. So, I just pushed the end of the filter to fit in the box. While I was doing that, I moved the filter like you would with the combination lock and it just fits in. (you will have to push the closed lid of the filter to fit the airbox as well- it was very painful... also broke the screws in that airbox). I had a Ford technician transferred the air filter to my 2014 Focus when i traded mine in.
 

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More air can equal more fuel burning.

Whaa?
Um it's simple combustion.... [poke] Edit: Let me explain... Colder air is denser than warmer air. So if you bring in denser air, the more gas that can actually combust. Our cars' ECU can actually adjust to these changes. The K&N drop in does bring in more air. With the stock intake setup being a cold air setup, that means that more fuel "can" be burned depending on driving style.
 

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Um it's simple combustion.... [poke] Edit: Let me explain... Colder air is denser than warmer air. So if you bring in denser air, the more gas that can actually combust. Our cars' ECU can actually adjust to these changes. The K&N drop in does bring in more air. With the stock intake setup being a cold air setup, that means that more fuel "can" be burned depending on driving style.
And the throttle controls the whole thing. So if you only introduce set amount of air you only use the same amount of fuel. Your decreasing a restriction . Which makes it more efficient . Wide open yes more air more fuel .
 

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And the throttle controls the whole thing. So if you only introduce set amount of air you only use the same amount of fuel. Your decreasing a restriction . Which makes it more efficient . Wide open yes more air more fuel .
So yes, if the OP has his foot down on it now, it will burn more fuel. Even with my normal driving, I noticed my MPG's down. As I had said in both posts, it depends on how he drives [driving]
 

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So yes, if the OP has his foot down on it now, it will burn more fuel. Even with my normal driving, I noticed my MPG's down. As I had said in both posts, it depends on how he drives [driving]
Nope . In normal driving the ecu keeps the stoichiometric mixture constant . That's why K&N ads proclaim fuel savings.
 

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A/F is not the only factor to this. Ecu makes many changes, A/F can still be a constant 12:1 even with more fuel and air. If the ecu sees more air, you can guarantee it will throw more fuel to keep the A/F constant as you said.
 
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