[HP Autosport]

Our high-flow air filter for the N55 is ready for in car testing.

Here is the top and bottom view of the filter.

Why Foam Is Better

The principles of how foam air filters work is simple: "Open Cell" Polyurethane Foam is wetted with specially developed filter oil. The "sticky" filter oil is suspended in the path of the dirty air on the strands of the web-like cell structure of the foam. This makes it impossible for dirt to pass through the depth of the filter without sticking to the strands. As the outer strands become loaded with dirt particles, the wetted strands down stream start trapping dirt, allowing the entire thinkness to be utilized. This prevents surface loading or air restriction for 80% of the service life of the air filter element. When the air filter is sufficiently dirty. It can be easily washed, re-oiled, and re-used.

Below is an independent dyno results by "FrankiE90" and a link if you guys want to read the full independent review:

http://www.e90post.com/forums/showpo...53&postcount=1

[cstavaru]

The problem is, BMS showed a 30whp drop when dynoing the car with the air filter removed. This is because the way N55 measures air via a MAF sensor. This means that a high flow filter is likely to be detrimental rather than beneficial to performance without a special MAF sensor calibration via electronics.

[wchoy]

hmmm interesting... lets see where this goes...

[benton0311]

Having run oiled filters on several other cars with MAF sensors they also bring about another issue: the oil residue eventually builds up on the MAF sensor causing faulty readings.

Usually not too hard to fix but it means that for optimum performance you need to remove and very carefully clean the MAF sensor to remove the oil residue at some point for continued accuracy. I got to the point where I would clean the MAF sensor every oil change but it usually takes a good bit longer for problems to show up. Usually will manifest itself with reduced fuel economy, slightly reduced power, poor idle, and a MAF sensor code when it gets too coated in oil.

[Ilma]

Originally Posted by benton0311

Having run oiled filters on several other cars with MAF sensors they also bring about another issue: the oil residue eventually builds up on the MAF sensor causing faulty readings.

Usually not too hard to fix but it means that for optimum performance you need to remove and very carefully clean the MAF sensor to remove the oil residue at some point for continued accuracy. I got to the point where I would clean the MAF sensor every oil change but it usually takes a good bit longer for problems to show up. Usually will manifest itself with reduced fuel economy, slightly reduced power, poor idle, and a MAF sensor code when it gets too coated in oil.

This is well intentioned, but also a shining example of how incorrect information keeps getting regurgitated by inaccurate and untested explanations.

I am sure everyone has seen the pictures of our intercoolers and intake pipes that are completely covered in oil residue from crankcase blowby.

There is far more oil contamination in the intake system from your own engine than there is from an oiled air filter.

Have a look here for some actual measurable testing on this:

http://www.knfilters.com/MAF/4MAFSensorVideo.htm

http://www.knfilters.com/MAF/3MAFSensorVideo.htm

http://www.knfilters.com/MAF/2MAFSensorVideo.htm

[benton0311]

Originally Posted by Ilma

This is well intentioned, but also a shining example of how incorrect information keeps getting regurgitated by inaccurate and untested explanations.

I am sure everyone has seen the pictures of our intercoolers and intake pipes that are completely covered in oil residue from crankcase blowby.

There is far more oil contamination in the intake system from your own engine than there is from an oiled air filter.

Have a look here for some actual measurable testing on this:

http://www.knfilters.com/MAF/4MAFSensorVideo.htm

http://www.knfilters.com/MAF/3MAFSensorVideo.htm

http://www.knfilters.com/MAF/2MAFSensorVideo.htm

ALL of the the engine contamination is post MAF sensor in any car. I'm not aware of any OEM (not saying it doesn't exist but I'm not aware of any) that mounts the MAF sensor after the PCV return, turbo, vacuum hoses or any other engine connected tube. Virtually all OEM MAFs are located near the air filter and pre-boost. There is no engine oil contamination on the portion of the intake before the PCV return hoses or turbo.

Thats's why when folks do custom blow thru MAF setups (after turbo) on built turbo cars (for when you want to retain the MAF low end drivability without the intake restriction) it is highly recommended that a catch can or air oil separator be used in order to prevent oil contamination of the MAF.

Also, while I have experienced oil contamination post filter with K&N setups you're also comparing the K&N to an oiled foam filter. Last foam filter I used, on a rotated turbo setup on an STI, was very heavily oiled and I saw visible oil residue in the MAF tube which was right after the filter.

On a side note, I don't think K&N's own testing on this subject should be considered the most unbiased. I have run several K&Ns in the past (Vette, WRX, STi) and have definitely had to clean the MAF sensor due to receiving MAF related error codes.

I'm not saying it was a big deal. Contamination really didn't start to become a problem on the K&Ns (actually two K&Ns and one Injen filter) until over 10k miles or more of use after new or re-oiling. And it was very easy to clean, just remove the MAF, spray down generously with MAF or electronics cleaner, clean the housing and exposed areas (not hot wires or MAF components) with a q-tip and be on your way.

[Ilma]

On the N54 at least, the MAP sensors are just in front of the throttle body and also in the intake manifold........

Therefore further downstream than the air filter and subject to lots of oil contamination from the crankcase vapours.

Besides, if you watched those videos I linked carefully, you would have noticed the comments about OEM's placing charcoal filters in the air box as a pollution control mechanism due to residual vapours migrating backwards into the intake system once the engine is shut down and making their way into the atmosphere via the the air filter/MAF sensor housing.

MAF contamination is not as simple and straightforward as you think it is.

It's always easy to blame the oiled air filters, but those videos show some compelling evidence that speaks otherwise and they base their conclusions on empirical testing.

Hope you caught that bit about a burn off cycle on the thermistor at start up to help burn off contaminants from the MAF.

[benton0311]

Still working on the videos, I'm 8,000 miles from high speed internet for the time being. Hoping to finish them by tonight. I do have to call into question the fact that K&N is putting these out. That and the fact that when you search for MAF oil contamination the top links that come up are ones that are clearly sponsored by K&N.

The MAP sensors should be a non-issue. They simply measure pressure and shouldn't be very prone to oil contamination, if at all. MAP: Manifold Absolute Pressure and in order to measure the correct pressure it has to be in or near the manifold and post turbo, intercooler, etc. If it was anywhere else it would only sense a vacuum.

Thing is I've actually seen the oil residue in the various MAF housings and on the inside of the filters and it wasn't engine oil. As for vapors coming back through the intake I'm sure that happens to a small extent when the engine is shut off but anytime the engine is running it is pulling air in under significant vaccuum.

Now, on the other hand, even though I saw non-engine oil in the filter housings maybe that wasn't the actual contamination that my MAF sensors were experiencing. In that case then it would have to be increase in particulate matter that was making it through the filters.

[HP Autosport]

Lots of MAF issues occur after people clean their filters and simply spray way too much oil on the filter element, more is not better in this case. When you can physically see the oil droplets, it's too much.

[FrankiE90]

for those wondering dyno of the foam filter at the link.
335 N55

http://www.e90post.com/forums/showth...53#post7788253

[D.B.S]

Nice Dyno numbers...

HP Autowerks... this is Probably a silly question, but this filter should fit the air filter housing for the X5 right? It's the same engine... I'll take a look later today and see if the housing is the same... should be... If so, I'll be ordering this ASAP...

[MikeDNJBMW]

trying to get an update from anyone else that have used this filter........any other reviews???

[HP Autosport]

Originally Posted by Army335xi

Nice Dyno numbers...

HP Autowerks... this is Probably a silly question, but this filter should fit the air filter housing for the X5 right? It's the same engine... I'll take a look later today and see if the housing is the same... should be... If so, I'll be ordering this ASAP...

If you can remove the filter from the housing, it shoudl have BMW part# 13-71-7-599-285 or Mahle LX 1791 on it. If those numbers match, it's the same filter. It only makes production sense for BMW to use the same airboxes for both cars.