K&N air filter
 

Is anyone using a K&N air filter in their car? If so, do you see any improvements?

Yes, I just installed mine about 1000 miles ago. Like with previous cars where I put one in, I immediately noticed a crisper throttle response and it feels like the engine is effortlessly breathing. I am a definite believer. The cost of a new factory filter is like $30 while the K&N is only like $55. And it is the last filter you will need to buy.

One note: the K&N for this model covers quite a few other models. I checked the K&N website and there is like 20 different applications for that filter. The reason I checked is because I thought I had the wrong one. The inside diameter of the K&N where it mates against the inner plastic tangs of the air box is slightly larger than the stock unit. I thought this would be a problem, but it was not. Just get it centered in there and the top and bottom halves of the air box compress the rubber to form a tight seal.

One other note: A friend told me he had problems with a K&N in his BMW because the oil in the K&N fouled up the MAS. He said this "could" happen. He also said the problem was easy to remedy with MAS cleaner spray found at local auto parts stores. Just make sure you clean the MAS the right way and do not touch it.

Look into the cost of a new MAF sensor so you can decide.

I've seen this miracle air "filters" dyno-ed quite a few times. Bottom line: save your pennies for something with a tangible payback ;)

Welcome aboard!

Without raining on anyone's parade :)

I have heard of evidence on other forums where more than a few turbo cars warranty have gotten voided because of 'dusted' turbos ....

so buyer please do your due diligence...

While I too have used K&N filters in the past.... won't on the newer engines given that the gains on the K&N are in the HIGH rpms where I normally only hit every once in a while....

And even the QUESTION of less filtering is not something I want to be paying for a new engine or turbo.... YRMV, just offering a cautionary note .

Performance deduct: Bosch, Hitachi and your local garbage co. will all like it.
 

More MAF sales and more stuff ultimately for the landfill.

They foul MAF's. Been There, Done That, on an Audi 4.2 specifically. On my 2000 A6 4.2, installed one, and in due course found the unmistakable telltale red filter oil a foot plus in an UPWARD direction in the intake tract, well past the MAF that is the very first thing after the air box. Also found it all the way at the throttle plate, which is probably 18" from the filter. Red oil doesn't just come in from no where.

To save posting response time for the normal one: yes, I know how to oil 'em sparingly. Irrelevant here anyway, since this was the FACTORY oil out of the box--the new ones come "pre-oiled." I used these for many years on non MAF cars, back to my 1973 C1 Audi with the Solex and then Weber carb. But, this first person experience is they don't work on MAFs, and I had eliminated the normal debated variable about supposed owner inexperience. Also to confirm, yes out of the box of course all was normal--it wasn't soaked in oil or anything. Looked just like many others I have seen when they are fresh.

Next one: the cleaners work so no big deal. Not. I took the MAF off. Several times. Cleaned it with rubbing alcohol one pass and sensor cleaner another. Even immersed it in rubbing alcohol for hours after I got it out of the plastic tube (another old C5 and 2.7T S4 board idea). Bottom line, didn't cure it. Since it is a hot wire set up, that's to be expected. The oil essentially gets cooked on there, coats the wire and then game over. Parts cleaner solvents (or alcohol) aren't typically going to do much once it was been baked on there.

And, how do I know it was no good? Well, with an Audi and VAG COM you can just monitor it. Rule of thumb is reading should be about .8 of the HP, measured in grams per second. I did that instrumented for about 30 minutes while data logging to the laptop, particularly at full acceleration to get max flow readings near shift point out of first and second gear. Flow reading was about 210 g/s max. 210/.8 implies 262.5 HP. Performance subtraction = as much as 37.5 HP ! Nice mod. Effectively the MAF is detecting less flow than is really there (since the motor is still mechanically pumping), and then would be running a lean mixture if it only relied on the MAF input. Likely the O2 sensors can correct for this within reason plus it knows the throttle position (car has an electronic throttle), but only with some lag in the case of the O2 sensor feedback loop.

So why in turn did I do the diagnosis and all? Obviously I needed to fix it. But, back then w/ the car only a few years old, MAF's could only be bought at the dealer. Like, $500+ new and hundreds of dollars even at a discount. Thus, I cleaned it several times trying to avoid that bill. Ouch.

And finishing the story, replaced the MAF with a new factory part. Immediately readings back to between 245 and 255 when instrumented the same way, i.e. at or over the 300HP that motor (a 2000) was rated at.

Bottom line for me: on an older pre-MAF car, have at it. On an MAF car, it's a performance subtract for me. And the hideous thing is, if you don't instrument it (I did because I had a tranny shifting issue that could implicate the MAF but was ultimately a broken sensor wire; thus I was diagnosing the MAF separately) you won't probably won't even know it given it will foul over time.

You have sufficiently scared me with your detailed analysis of the issue.
I've had K&N filters in for about 7K miles, and hope that by having two of them there is less suction per square inch, and therefore no oil migration.
I'll do an inspection soon, thanks.

MP4.2+6.0
 

best reply ever MP4.2+6.0
it's been documented a million times they don't work for crap, but cause expensive repairs down the line.
I personally refrain a lot from posting these things because the average inexperienced person will believe anything and the person who has them will swear they work amazingly.
is plain common sense, if by installing these filters you could get even 2% more horsepower the factory would install them, but as you know there are a lot of geniuses here that will argue without having any actual facts.

And this is why I appreciate this forum so much. There is a lot of very valuable experience gathered here. Excellent write up MP4.2+6.0. Thanks for taking the time. And, since you and s4master1 are in agreement, I'll take that as the gospel. ;)

I've read posts on other forums (other makes) about the same K&N oil issue. So, it isn't just an Audi thing. It's all definitely enough to put me off the K&N route for my ride. Other (older) cars, no problem. But, not my Beautiful Beast.


Carry on...

I've used my K&N since 54k miles. Now at 90k. No issues so far. Don't notice a difference between stock and K&N.

School of Hard Knocks
 

These are very astutely stated arguments against K&N for MAF vehicles, particularly MP4.2+6.0. However, I am not totally convinced. Admittedly, I may be when I have to buy a new MAF.

Here is the thing that makes me pause to buy into the current dialog completely: I used a K&N on my Toyota T100 with a MAF for over 100,000 miles of driving around the country with no adverse effects. I had probably cleaned and re-oiled it 4 or 5 times, never cleaned the MAF. I did not have oil in the air induction tube or on the MAF. In fact the K&N filters more particulate when it gets used a bit (while it still sucks more air than a standard filter). And, the air tube stayed very clean in my experience.

Now what I did not do is test the Toyota MAF with a VAG-COM like device, so I cannot accurately say if the MAF was getting a lower reading like MP4.2+6.0 says. But I did not ever feel that there was a reduction in performance. I always felt a crisp throttle response.

For me the jury is still out, and I will continue to use it and monitor the MAF. Best case, I continue to benefit from more available air flow and don’t need to buy another filter. Worst case, I learn a lesson that cost me a new $30 filter and $200 MAF sensor.

I am an avid mountain biker and participated in mountain bike forums for several years. I have learned a tremendous amount there from people who had experience that varied or was vaster than my own. However, I have also been lulled into paranoia about topics when I read a particular thread that seemed to present a valid argument that later turned out to be totally untrue. One example was a special crank face alignment tool I remember thinking after reading threads that was absolutly required to install a HammerSchmidt crankshaft. The tool cost like $500 and could not be found. It seemed like on the threads I read that you had to have it or else you were doomed. But it turns out no one had it because it really was very rarely needed. I installed the crankset without it and the system has worked perfectly since.

Experience is still the most dependable investigator. Most importantly, when using that experience to interpret another’s.