Been meaning to post this for a while. First picture shows aftermarket K&N type filter that I removed as part of my super charger install - seems to be doing its job looking at the colour and amount of crap stuck in it.

Second picture shows crap that had managed to get past the filter and was only stopped by the mesh over the MAF. Question is how did it get past the filter? My airbox is undamaged and all straps are in place.

 

I noticed the same thing when I was using K&N. I switched back to a stock filter and it hasn't happened again. Not sure why the K&N allows that stuff to get by, but I know that it doesn't fit the airbox as well as the OEM filter.

 

I don't believe that the bits went throuigh the filter, Bert. The K&N fits a Euro S2 airbox OK, but the ones I have seen on an S4 and later, with the shallower lower airbox are very difficult to fit correctly. What usually appears to happen is that the rear of the filter does not engage properly into the airbox bottom and so there is a gap.

 

The KnN filter will bleed oil into the MAF wire and over time this will contaminate the MAF, the factory filter fits the airbox better and flows/filters more air due to the bigger filter surface than a KnN , recommend to get a factory filter and change it when necessary , the rest of your injection/induction system will last/perform better/longer..........Also there is a possibility that since the KnN doesnt fit as well big pieces of dirt seem to fall into the filter base due to the poor fit along the rear of the filter housing, and this is made worse by the fact that the Rubber hold down clamps are pretty streched out after 15 to 20 years of service

 

you guys dont read my posts do you !!!!!

the air leaks for the intake box will allow stuff to get in from around the sides of the filter.

the filtering capasity of the KN vs stock is near the same, however, there is less restriction with the KN. no gains will be seen however, if there are air box leaks where "stuff" can come in around the sides. I measured .25"Hg vacuum in the air box , with only 290rwhp, however, this jumps to .5"Hg with the air box filter sealed! MEANING, there was a major leak before under WOT conditions.
MK

 

Don't get your knickers in a twist !

We are all saying the same thing - K&N is a crap fit, so bits get direct into the MAF.

 

Oh well, its gone now! I checked the filter and you can actually see from the imprint of the filter housing where the poor fit occured. Lesson learned - buy supercharger sooner next time.

 

I used the shorter old style 911 straps on my air box with my K&N. It's a real tight stretch to get them on but it snugs things up real tight.

Surface area is only one component of flow rate. You also have density and thichness of material. Having more surface area alone is not a garauntee of higher flow. The K&N flows better than the stock filter. Fact. However it does so by having a less dense filter media, allowing for less filtration. It's a trade off. The stock filter flows fine for any HP requirements any of us on this page have had. At anything less than WOT the filter makes little difference on HP. I went K&N to save money over the next few years. Don't think I realized any HP gains, but hey, the sticker looks cool on my car

As for oil damaging the MAF. I'm not convinced, too many cars use it fine. I think it may be operator error from over oiling during instal. Follow the directions and you'll be fine. Any minute amount of oil that covers the MAF will be burnt off of a properly functioning MAF.


Also when were K&N filters green?

 

Yes agreed, K&N filters are crap to begin with, and on top of that they don't fit the 928 airbox well, which defeats the purpose when it inevitably allows big particles to get around it. There is one on my new car, I will replace it with stock next tune up.

 

http://www.green-filter.co.uk/

 

Bert, you learned your lesson well!

My PO put the air filter in upside down, so I also did not have a great airbox seal, and also found a couple of pieces of debris on the mesh screen when I replaced it with a new one today.

 

The K&N's get a bad rap, IMO. If they are maintained correctly, they deliver the goods.

Having said that, I removed mine and went back to a stock filter because there was no need to run one. But, I run a cone-shaped oiled filter on my 911 to clean up the bay and lose the monster airbox. Clean them regularly, and oil them PROPERLY, and they aren't "crap".

 

The cone ones may be better, but the stock replacement ones have fitment issues (have seen several like this) which is more of a problem than the filter element itself. Maintain it all you want, but if it doesnt fit well to begin with thats not good. I also think the wire mesh is shoddy with inconsistently sized air holes and loose bits of wire that look like they could break off into the intake. I still think theyre 'crap'

 

That said, I'm not a 'purist' regarding this stuff, I use BMC filters (similar design to K&N) in my bikes with good results, but I don't think they make them for cars.

I'll take the filter on my new S4 apart and look at it to see how it has performed, who knows, maybe better than I expect to find.

 

This is an annual beach and moan topic.
IMO the K&N has gotten the same deal Joe Wilson and his wife got PLAME GATE...
I recall Wally P. -much revered/respected GURU- claiming that there were major bug parts in the
mesh. So be it, but from his description, at the time, one would believe that the bug went thru the filter.
At the time I had just pulled the filter/box and airflow sensor -aka air flow meter AFM- to more easily access the rear spark plugs. this offered the opprotunity to do a fair clean-up of a buch of things including the AFM which was filthy inside and out with a oem paper filter upwind. So I spent a couple hours getting everything sparkling clean and installed the NEW K&N.
I might point out the damn thing was absolutety dripping with oil and had clumps of lube all around it -both sides. I completely cleaned it relubed then set it in the sun. Wiped then wrapped it in an old towel and dropped it to the floor from 2 feet to dislodge any 'clumps'. Installed it then drove as usual,
which is to say beat her like a rented mule. I had been ramp to ramp, roll on racing at the time...often.
And had occasion to see the far side of 140mph -extended runs/35-50 mile- a few times as well.
At first I checked the filter and things downwind at 2000 mile intervals to include white sock wipe downs of the AFM throat/gate area. CLEAN!
Eventually, extended inspections to 4K miles...Clean!
When I mentioned this to Wally in a post I got mildly hammered.
Since the bug part story came up again I mentioned proper install/seating.
Wally thought I was hacking his air filter install ability
When the hot-wire issue appeared I recommended not using it on MAS equipped sHARKs,
though I believe over oiling is the issue. Keep in mind those hi-rpm/140 plus mph runs
where I had NO oil coating in the 'throat' area. However, I agree ,hotwire only, that the cost of a fried or baked wire is not worth the expense should oil 'get by'.
You can hit particulate/filter test sites that will will both prove and disprove which ever side you take...
From my perspective, there is no issue at all for the AFM -OB- equipped sHARKs.
BUT, there may be an issue for the hot wire equipped sHARKs, so don't use it!
But the annual crap blowing festival really needs to go away.
There is no justification for dumping on a product that works if lubed and installed, and secured properly on the the AFM equipped 928's.