Your Thoughts on the use of K&N filter?
 

I wanted to get some feedback on the use/issues with K&N Filters. I was doing some research on replacing my MAF and I came across people saying that K&N Filters (If using them) are one of the issue that cause the MAF to start acting up due to the oil from the filter?

Anyone can confirm or dispute this claim or offer alternative to these filters?

thx :dunno:

The K&N filter uses oil on the foam to help filter. Too much oil can damage the MAF. It is well documented that it can happen. When the oil is properly applied, ie not too much, that specific problem can be avoided. Note that the filtering efficiency depends on the oil being properly applied. Also, the filter holds less dirt, ie it gets clogged more easily, so servicing needs to be done more often than with an OE filter.

The second potential problem is codes being thrown. It can happen. It is usually related to vacuum leaks.

The bigger questions in my mind are:

1) Why would you want less filtering capability? Lots of tests show that the K&N filter isn't as efficient at removing dirt. If you don't care about the filtering, just take the filter out. That is the lowest possible restriction, although it will be bad for your engine to ingest dirt.

2) Why worry about the minimal amount of restriction caused by a functioning air filter? It is completely irrelevant in terms of power production.

Some additional reading if you like. Follow the links here:

http://www.xoutpost.com/794434-post4.html

Edit: I checked the links in that post, and one is broken. Here is another link to the Duramax filter test with graphs of K&N filter efficiency compared to an OE:

Aftermarket Air Intakes/Filters - Do They Work? - Diesel Place : Chevrolet and GMC Diesel Truck Forums

Thanks JCL....very informative feedback.

I've had one fitted for 6 years without any trouble...

Note that the review link was for a diesel truck site. Diesels run at lower RPM than gasoline engines, and airflow is less crucial at lower RPM. My Boxster @ 7500RPM is sucking a lot more air than my X5 @ 5000RPM.

I don't see any reason to run a K&N filter in a diesel X5. If my X5 was gasoline, I'd check the CFM rating of the OEM filter vs. the aftermarket filter, then find out what the CFM requirements of the engine are at max RPM, and THEN decide if the K&N was worth the cash. In almost all cases, it's probably not worth it.

I run a K&N in my Corvette, but I also have a hacked airbox, free-flowing exhaust, and long-tube headers, so the motor can actually make use of the additional airflow. Switching to a different air filter without making any changes to the rest of the intake/exhaust system is, once again IMO, a waste.

Yeah, I used the diesel engine filter test because it is good comparative data. Engines are just air pumps, whether they are compression ignition or spark ignition. And those diesels have more displacement, as well as a lot of boost, resulting in high airflow requirements regardless of peak rpm. That is why the diesel truck owners spend a lot of time discussing intake modifications and filter efficiency, and conducting tests such as this one. Building on your point about exhaust flows correlating to intake flows, that is why diesel pickups have large diameter exhaust systems, because they are flowing so much.

Good point about the larger-displacement diesel engines... I was, of course, thinking of MY diesel, because I'm a self-centered BMW owner. :D

To answer the original poster's question (again, since I got carried away due to my self-centered BMW driver ego... heh) - you won't see any perceptible gain from the K&N. While a new properly oiled filter won't foul your MAF, recharging it yourself and doing it wrong often does. Spending additional money that may wind up costing you even more money - for no perceptible change except the addition of a K&N sticker - isn't worth it.

Replacing the soiled OEM filter with a new OEM filter is a good alternative.

:iagree: 100%

Waste of money.

So don't waste your money.

:iagree:. Waste of money.

had one since summer 2008, no problems. And i picked up a couple extra MPG on an average with my 4.6 over the dealer installed filter. I've seen road trips in the 24-25 mpg range. (i was being VERY mindful of throttle usage). If i had a 4.4's gear set, 30 mpg would almost be in my grasp.

no that wasn't an invitation to swap for anyone who's thinking that.. haha.

What about the AFE dry filters?

Long
 

I don't have independent test data on the AFE Pro Dry filter in this specific application, but there is some info available by searching, and some reasonable conclusions can be drawn from the links I posted above. This doesn't just apply to the AFE dry filter, or the AFE oiled filter, it applies to a whole class of aftermarket filters that are claiming increased airflow as a selling feature.

1) This is a dyno test of the AFE filter vs the stock filter in a BMW. No hp difference was found. I would fully expect that result, see point 4 below.

Dynometer test AFe versus OEM Filter... - BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3)

2) This is an ISO 5011 test of the AFE dry filter. The stock paper filter in this test was a Mopar. The AFE filter had a reduced filtering efficiency (it literally let in twice as much dirt), and held less than half as much dirt before being clogged, compared to the stock paper filter. This is consistent with other tests of stock paper filters, for several manufacturers, see below. Test results here (in the psm link click on evaluation results to see the figures:

http://www.psmdiesel.com/afe_air_filter_2nd.php

3) This is an ISO 5011 test of the AFE dry filter. There are various comparison filters and inlets included in this test, but I focus on the stock AC paper filter, the first test. The AFE filter had a greatly reduced filtering efficiency, and a greatly reduced dirt capacity (96 grams vs 588 grams) prior to clogging. These types of non-paper filters will typically only have their better claimed airflow when new and clean; the restriction curves are exponential with increased dirt and not linear like paper filters. That is a generalization, but it is shown repeatedly in the graphs in the link in point #4, below.

http://www.sbfilters.com/site/pdf/IS...y_75-80882.pdf

4) So, the background info suggests that the AFE filter can flow more air than stock, as AFE claims. Also, it shows that the filtering efficiency and dirt capacity, two critical performance measures, are reduced over stock. This is consistent with a non-paper filter compared to a paper filter. What you are gaining for these trade-offs is the ability to clean the filter instead of replacing it. At this point I would go back to the link I provided in post #2. The short version is quoted in this paragraph:

Full test here: Aftermarket Air Intakes/Filters - Do They Work? - Diesel Place : Chevrolet and GMC Diesel Truck Forums

So, my own summary observations, with this testing listed above as background:

a) A real filter test should be run to the ISO 5011 spec. It is a very controlled test. It is not often done by filter sellers. SB, linked above, appear to be one of the few doing that test. AFE, like many other manufacturers, instead use their own tests and graphics on their web sites. Why? Because they are promoting a single feature (such as maximum airflow) instead of acknowledging that everything is a trade off. A filter is there to remove dirt. If you let more dirt in, and cause more engine wear, is that a good trade off? If the filter only flows more when new, but clogs up 8 times faster (quickly reaching the increased restriction level during that cycle) is it at all relevant to say it flows more on a test bench?

b) The maximum restriction through the whole system caused by the air filter itself is marginal. Claiming that a filter can flow more, while not allowing more air to reach the filter through the filter intake, or exit the filter through the engine intake, or exit the engine through the exhaust, is of no value.

c) So what is the upside? Why take on the risk? Installing any aftermarket filter that claims to increase airflow can reasonably be presumed to increase dirt ingestion, and can reasonably be assumed to not impact hp or fuel efficiency over a clean OE filter (unless the engine and exhaust are significantly modified to take advantage of any increased airflow capacity).

d) Buy an OE filter.