[FormerRotor]

Evening, Ladies & Gents,

I've been considering removing the foam "pre-filter" piece from my engine air filter for some time. It has always been my opinion that it is there more for acoustic dampening than for actual filtration. My only concern has been that fully removing the foam piece could somehow affect the seal of the filter against the box and therefore increase the pressure at which the spring loaded secondary intake in the box would be activated.

I'll start by saying that I am over-complicating this and you could probably just rip off the foam piece without any adverse effects, however, this is how I decided to proceed...

• I installed my new filter and left it in the car for a week so that the box would make a clear indentation on the foam.
• I then pulled the foam almost entirely off of the paper element, leaving the area of foam which sits over the secondary springloaded section and the indentation intact (glued)
• Next I cut around the indentation leaving about 1 cm between the indentation and the cut.
• The final result was a filter which has a naked paper filter on the primary section of the box but retains the pre-foam filter on the seconday section of the box (really just for the sake of the "seal").
• I then reinstalled the filter and started the engine.

Ze box...

Ze filter...

Ze modification...


Results? Believe it or not, there is a very mildly increased intake noise with a small bit of added grumble. It is (to me) only noticeable when outside the car or with the windows down, but I asked my wife to tell me if she noticed anything different and she stated that the car sounded "angrier". Were you to emulate the above...if you rev your car while parked before and after, I think you'll notice a slight difference as well.

I would imagine that the difference is similar to that of adding a K&N filter, but without the filtration concerns that come with the K&N (for some). For a free 90-second modification, I'll take it.

[335dFan]

I really enjoy reading all these posts demonstrating our passionate love affairs with our cars. Only we would get it I guess.

[Julesandtrish]

FormerRotor, can you post a pick for clarification? I have a picture in my head of what you describe, but I just want to make sure. Thanks in advance.

[FormerRotor]

^Yeah, I tight about it the second that I dropped the hood. I'll take a pic in the morning and add it to the original post.

[Julesandtrish]

Cool. Thank you sir.

[FormerRotor]

Originally Posted by 335dFan

I really enjoy reading all these posts demonstrating our passionate love affairs with our cars. Only we would get it I guess.

Yes, I suppose we are a bit fanatical, aren't we? I've really enjoyed going back and reading the old posts on this forum from the diesel pioneers (TDI and the likes). I was one of the first in my area to take delivery of a rx8, so I often forget that a lot of guys have been at it with the diesel for 3-4years already.

Originally Posted by Julesandtrish

Cool. Thank you sir.

My pleasure, but you might not want to thank me until I don't forget to do it.

[Julesandtrish]

FormerRotor, can you elaborate on how the secondary spring loaded section of the air filter box works? I see it, but don't understand how it works. Does it help blow off water/fluids that get in there?

[Got_Diesel]

I pulled off the old foam paper on my air filter once it got dirty and it worked just fine.

From what i know, that foam paper is only used for snow.

[FormerRotor]

Originally Posted by Julesandtrish

FormerRotor, can you elaborate on how the secondary spring loaded section of the air filter box works? I see it, but don't understand how it works. Does it help blow off water/fluids that get in there?

Edited OP with pics for your reference J&T.

I'm obviously not a BMW design engineer, but it seems to me that the spring was likely selected to be compressed at a certain negative pressure to allow air into the box from the engine compartment. This would likely be useful if the intake were clogged so that the engine is not choked out.

[Got_Diesel]

Originally Posted by FormerRotor

I'm obviously not a BMW design engineer, but it seems to me that the spring was likely selected to be compressed at a certain negative pressure to allow air into the box from the engine compartment. This would likely be useful if the intake were clogged so that the engine is not choked out.

Correct. If the intake gets clogged with snow, the other warm air intake opens and lets air in. I believe VW does this too.

[sohcpunk]

I wonder how the dealership will take this when they change out your filter to find it's been "modified". Wouldn't they note it down and if something were to happen to the engine in the future deny warranty?

[FormerRotor]

Originally Posted by Got_Diesel

Correct. If the intake gets clogged with snow, the other warm air intake opens and lets air in. I believe VW does this too.

Thanks for the confirmation, gd! At first, I wasn't sure what you meant by it "being for snow". I thought you were alluding to the foam and got a bit confused

Originally Posted by sohcpunk

I wonder how the dealership will take this when they change out your filter to find it's been "modified". Wouldn't they note it down and if something were to happen to the engine in the future deny warranty?

I have a spare one in the garage that I can always toss in. If you are in- warranty, then they would have to prove that this caused the failure (highly unlikely). If out of warranty, then it may cost you some leverage when looking for concessions.

You are not removing any filtration capability by removing the foam and the actual filtration media is the pleated paper filter behind the foam. Te only thing you may be doing is causing the filter to load more quickly as you are reducing the surface area (but the foam is porous enough that it is really only catching the big bits). If they were smart enough, they would likely feed you some bologna about how the foam disrupts the cavitation of airflow in order to more evenly disperse the air over the filter media and allow more regular flow over the MAF (but this would be bologna), especially considering that they have many other vehicles with newly identical box design and only a paper filter (no foam).

[Puerto Rican 335d]

Rotor I hv not forgotten you I will try to send pics today ok Im under construction at my home

[FormerRotor]

Originally Posted by Puerto Rican 335d

Rotor I hv not forgotten you I will try to send pics today ok Im under construction at my home

Haha. No worries, PR. This is all of our "second lives", the primary has to take priority. Talk soon! What kind of work are you doing?

[Puerto Rican 335d]

Expanding closet to garage to add either a Diesel or Gas(Natural) Generator and hang my bikes there!!

[FormerRotor]

Originally Posted by Puerto Rican 335d

Expanding closet to garage to add either a Diesel or Gas(Natural) Generator and hang my bikes there!!

Nice! I love me some garage work

[Puerto Rican 335d]

rry amigo having issues with neighbors about the garage issues i am within the required parameters of construction and they're stating i have it wont , would you believe that they came at 7:30 pm to complain needless to say I tod them I was NOT coming down from my 2nd floor house to see at that LATE any inuendos i am within the property guidelines, Ive contacted the Complex Administrator and an Filed ngineer friend of mines and both state I doing everything correctly, People can be such wads, what eats me is that I know I am doing things correctly and people are trying to falk w me. I'll keep u posted Im sorry I hvnt sent you the pics but will try today ok

[GSXR]

Just out of curiosity, does anyone have the k&n drop in filter? I'm a new member lurking (hopeful future owner) and am surprised at the aftermarket availability (US) of this engine, I'm used to the cold air intakes and the only drop in k&n filters Ive used where on my bike but I have never owned a forced induction vehicle so does anyone know if it would be similar results to remove this foam piece as opposed to getting the k&n drop in? Either way, it is a pretty good free mod

[FormerRotor]

Originally Posted by GSXR

Just out of curiosity, does anyone have the k&n drop in filter? I'm a new member lurking (hopeful future owner) and am surprised at the aftermarket availability (US) of this engine, I'm used to the cold air intakes and the only drop in k&n filters Ive used where on my bike but I have never owned a forced induction vehicle so does anyone know if it would be similar results to remove this foam piece as opposed to getting the k&n drop in? Either way, it is a pretty good free mod

Candidly, I don't think either are really going to give you any gains that would be larger than what could be considered a testing error on a dyno (or even close there-to). Some folks do have k&n, but others believe that the cost of possible reduced particulate filtration and possible oil issues are not worth the possible benefits. Many here in the diesel section cite the Spicer report.

What's keeping you from buying the diesel? we'd welcome you to the dark side

[FormerRotor]

Originally Posted by Puerto Rican 335d

rry amigo having issues with neighbors about the garage issues i am within the required parameters of construction and they're stating i have it wont , would you believe that they came at 7:30 pm to complain needless to say I tod them I was NOT coming down from my 2nd floor house to see at that LATE any inuendos i am within the property guidelines, Ive contacted the Complex Administrator and an Filed ngineer friend of mines and both state I doing everything correctly, People can be such wads, what eats me is that I know I am doing things correctly and people are trying to falk w me. I'll keep u posted Im sorry I hvnt sent you the pics but will try today ok

Yah, that's one of the big pains of construction. Doing it right is fairly easy. Repeatedly having to prove that your work is being done right is a pain. If you don't have a good relationship with them anyway, just tell them to call the complex administrator if they have any concerns,

[GSXR]

Originally Posted by FormerRotor

Candidly, I don't think either are really going to give you any gains that would be larger than what could be considered a testing error on a dyno (or even close there-to). Some folks do have k&n, but others believe that the cost of possible reduced particulate filtration and possible oil issues are not worth the possible benefits. Many here in the diesel section cite the Spicer report.

What's keeping you from buying the diesel? we'd welcome you to the dark side

Well I HAD a bike, ate it, broke another collar bone lol and it was going to cost more than a grand to fix the bike minus plastics, it was already salvage so I figured ill just sell it and get a car but waiting till I start work in April when I recover, unless I find the right one, not that many with low miles right now

[FormerRotor]

Originally Posted by GSXR

Well I HAD a bike, ate it, broke another collar bone lol and it was going to cost more than a grand to fix the bike minus plastics, it was already salvage so I figured ill just sell it and get a car but waiting till I start work in April when I recover, unless I find the right one, not that many with low miles right now

10-4. Broken collarbone is pretty miserable, but I'm glad you made it out with just that. Good luck finding the ride. It's tough to find exactly what you want with the diesels in the used market, but definitely opt for sports package.

Out of curiousity, why go from a gixer to a diesel bimmer? I would've suspected a pure sports car if its a bike replacement.