E90 - K&N Air Filter Installation & Review

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#1
Okay, This is for Katsbimmer who was asking for help where the thread was closed by the Moderator (No flaming please):
This was taken from a e90 forum that I would like to share with Kats if she haven't done it yet.
superbass said:
Hey everyone,

I finally installed the K&N air filter tonight and here's my findings. First, as an installation note, you MUST remove the entire air box housing from under the hood. I didn't know that at right away, but it became pretty obvious after a few minutes that there is NO WAY to reach the Torx screws that are on the BOTTOM of the air box. Removing the air box requires removing two bolts that hold the top of the air box to the frame, then you have to detach the front left part of the air box from a rubber "accordian" leading from the air intake. Then you must loosten a round metal band clamp that is holding the edge of the rubber air hose leading from the rear of the air box to the throttle body. All in all, this process took me about 45 frustrating minutes because you have to wiggle and twist the air box carefully to free it from the rubber hose. Once you detach the box, then it's easy. Remove 6 Torx screws, take the air box lid off, remove the stock paper filter and drop in the K&N filter, screw it back together and put the air box back in the car.

Findings/observations

After putting the K&N air filter in, I started the car. There wasn't any discernable difference in engine sound or muffler sound when I revved up the gas, so I took it out for a little test drive. Well, here's the good (great) news. I felt that the car instantly had a little more pep, and also there was more of a "whooshing" sound when I got the RPMs past 5500 up to redline. I never heard that sound before, as I have been making careful observations about certain sounds and stuff ever since I got the car about 1 1/2 months ago. You really have to lay into the gas to know what I mean. When I was in 2nd gear, I really mashed the gas, but not all the way to the floor, and the car was really moving. And as I was mashing the gas, I decided to step the pedal all the way to the floor and there was like another sudden "surge" forward and the car accelerated even harder... weird!!! It felt like a downshift, but it couldn't be because the car was still in 2nd gear only! I guess the extra airflow from the filter caused the car's computer to change the air/fuel ratio and burn more gas. After, I returned from my little test drive, I noticed a different smell coming from the exhaust. It wasn't a bad or burning smell, but just different than I was used to. I've driven the car pretty hard before, but afterwards it never smelled like that.

Conclusion

I think that my $50 was well spent on the K&N air filter. I felt more performance, and got a little extra sound when you really mash it. Everyone should definitely think about dropping in one of these things.
 
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Big Daddy

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#2
She/he posted that it was done, they completed the job:

ok!!! so here we go...i just thought maybe someone here already did this mod. on an 06 325i...and they could give me some tips....but i did it already... "yes myself "... for those who didn't think i could!!!!heres how...1) its easier to remove the whole airbox...2) there are 6 screws they go all the way around, no way your getting your hand to all of them with the box in the car 3) two bolts on the right hold the box down, loosen the clamp at the rear and unplug the wire 4) remove the box, take it apart, change the filter...thats it!!!......thank you for those who had faith in me to get it done.....and as one of you said..."i wouldn't want to rush into something on a $40,000 car until i knew what i was doing!!!!!!".. thanx, glen
 

epj3

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#4
Wow the first time I've ever heard of a gain in power from a K&N air filter. Pretty cool, they must have changed their manufacturing process or something.

http://home.usadatanet.net/~jbplock/ISO5011/SPICER.htm

There was a link somewhere that they compared the filters for a M50, and the stock filter was by far the highest flowing AND best filtering, K&N was below the cheapo pepboys brand in terms of flow and filtering ability. But the K&N is worth if if you are going to keep the car for a long time.
 
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#6
JCsE46 said:
Oh okay!! Sorry to repost this and I didn't read the whole thread. Big Daddy, You can delete this thread if you prefer.
Its good that its here now, a person can always use the search feature in case we have a new member come across the same ordeal.

K&N filters are worth it, I put one into the Rover, definitley a preppier car now.
Its also worth looking into a cold air intake, I made a custom intake for the ML, 3.5'' pipe with a gigantic filter. Let me just say, oh my.. what a F-in big difference. At least a 10-12hp gain. More Air (cold) = More power =D
 

epj3

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#7
Militant-Grunt said:
Its good that its here now, a person can always use the search feature in case we have a new member come across the same ordeal.

K&N filters are worth it, I put one into the Rover, definitley a preppier car now.
Its also worth looking into a cold air intake, I made a custom intake for the ML, 3.5'' pipe with a gigantic filter. Let me just say, oh my.. what a F-in big difference. At least a 10-12hp gain. More Air (cold) = More power =D
Dude no offense but if mercedes engineers allow an AIR FILTER to be so restrictive that replacing it with one MARKETED as being better would "Free up 10-12 hp"... well, one must wonder if their engineers are french, and what kind of clown college they went to. [rofl]
 
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#8
epj3 said:
Dude no offense but if mercedes engineers allow an AIR FILTER to be so restrictive that replacing it with one MARKETED as being better would "Free up 10-12 hp"... well, one must wonder if their engineers are french, and what kind of clown college they went to. [rofl]
Actually you're wrong, the standard airbox is very well designed, it has a ram air intake through the front grill and another one from the wheel well. The filter isnt paper either, high quality stuff. The cold air intake I put was MASSIVE. I'll take pictures once I put my own pipe in.
 

epj3

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#9
Militant-Grunt said:
Actually you're wrong, the standard airbox is very well designed, it has a ram air intake through the front grill and another one from the wheel well. The filter isnt paper either, high quality stuff. The cold air intake I put was MASSIVE. I'll take pictures once I put my own pipe in.
Nah K&N is bullshit.

Jim Conforti (AKA the Land Shark) did some testing:
This was a scientific test, not one done by filter manufacturer X to show that their filters are better than manufacturer Y. The test results are pretty irrefutable as the test lab tests and designs filters where "screw ups" are absolutely NOT allowable (I can't say any more for security. Think "Glow in the Dark").

A scientific test was done on TEST filters where air was loaded with ACCTD (some standardized "test dust" called AC Coarse Test Dust) and sucked through the TEST filter then through an analysis membrane. From the Quantity of dust injected and the amount that gets through the TEST filter and is then captured on the analysis membrane we can calculate the efficiency of the TEST filter in Question.

BMW Stock Filter, Eff. Area of Media: 8.4 sq ft.
K&N Replacement, Eff. Area of Media: 1.6 sq ft.

The filters are the SAME size. They both fit in the STOCK BMW M3 airbox. The difference is that the STOCK filter has 65 pleats 1.5" deep and the K&N only 29 pleats each 0.75" deep.
Now, remember this ratio: " 5.25:1". It's the ratio of the AREA of STOCK to K&N. It's very important and will come into play later.

The STOCK filter efficiency started at 93.4% at 0 loading and increased to 99.2% efficiency as the loading increased to a max tested of 38.8 gm/sq ft of dust.

The K&N filter efficiency started at 85.2% at 0 loading and increased to 98.1% at the max tested loading of 41.38 gm/sq ft.

Now, I hear you. "Jim, that's only a FEW PERCENT". But is it?

Let's look. If we had 100 grams of dust on a new BMW filter we would let through a total of 6.6 grams of dust in. If we used the new K&N filter we get 14.8 grams of dust. That's 224% (TWO HUNDRED TWENTY FOUR PERCENT!!) more dust ingested initially, stock vs. "free flow" and this ratio is pretty much held. Somewhere between 200-300% more dirt gets "ingested" anywhere across loading equivalence. The more INTERESTING thing is when you look at what happens to the DP or Differential Pressure at a constant airflow as you dirty both filters equally with time.

The test used a rate of 75gr of dust per 20 min. Here's where the AREA difference comes MAJORLY into play. See, even though the BMW filter flows a bit less at the SAME loading, it also LOADS UP 5.25 times SLOWER due to it's LARGER effective area. So what happens is that the K&N initially flows better, but as the dirt continues coming in, the K&N eventually flows WORSE while still letting MORE dirt in.

Now, does any of this additional dirt cause problems? I dunno. I suppose we could have a few people do some independent oil analyses on different motors using both K&Ns and Stock filters. Get enough of them, and you'd have a good statistical basis. For me though, it's simple: More DIRT = BAD.

The additional short-term airflow might make sense on a track car. IMHO, it doesn't for the street.

-- Jim Conforti
Sorry, but I have to trust Jim's findings more than a manufacturer's claim. He only talks about dust - but there is an article out there somewhere where the people took filters apart and found the K&N was less efficient throughout its life in terms of air flow than the cheapest pepboy type of filters.
 
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#11
Militant-Grunt said:
Its good that its here now, a person can always use the search feature in case we have a new member come across the same ordeal.

K&N filters are worth it, I put one into the Rover, definitley a preppier car now.
Its also worth looking into a cold air intake, I made a custom intake for the ML, 3.5'' pipe with a gigantic filter. Let me just say, oh my.. what a F-in big difference. At least a 10-12hp gain. More Air (cold) = More power =D
Rofl, dude wtf are you doing to that car. You said it yourself, the ML has a great ram air intake setup. Just replace the stock air filter and you're good. The ECU dumbs down any benefit of the extra air it is taking in. You need air intake, exhaust, and a new ECU programmed to work with the two to get any benefit.
 

epj3

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#12
Here is what I was initally looking for. It's a test on E30 filters. (not an extremely accurate test, but it COMPLETELY agree's with other tests you can find on the internet!) Yes - it's for e30 filters, but ALL airfilters are practically the same, and the design of the air filters have not changed.

http://www.bolhuijo.com/airflowtest/
 
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#13
epj3 said:
Here is what I was initally looking for. It's a test on E30 filters. (not an extremely accurate test, but it COMPLETELY agree's with other tests you can find on the internet!) Yes - it's for e30 filters, but ALL airfilters are practically the same, and the design of the air filters have not changed.

http://www.bolhuijo.com/airflowtest/
Blah blah blah.

All you gotta do is get a a G-Tech Pro and test your car out. Then drop in the K&N and test the car out again under the same conditions and see if there are any gains. Chances are, there'll be something because you're initially changing your air filter probably because it was dirty.
 


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