Your Thoughts on the use of K&N filter?

[TravsX5]

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.

[romeokc10]

What about the AFE dry filters?

[JCL]

Originally Posted by romeokc10

What about the AFE dry filters?

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:

Originally Posted by Arlen Spicer

“The reason I started this crusade was that I was seeing people spend a lot of money on aftermarket filters based on the word of a salesperson or based on the misleading, incomplete or outright deceiving information printed on boxes and in sales literature. Gentlemen and Ladies, Marketing and the lure of profit is VERY POWERFUL! It is amazing how many people believe that better airflow = more power! Unless you have modifications out the wazoo, a more porous filter will just dirty your oil! Some will say " I have used aftermarket brand X for XXX # years with no problems. The PROBLEM is you spent a chunk of ching on a product that not only DID NOT increase your horsepower, but also let in a lot of dirt while doing it! Now how much is a lot? ANY MORE THAN NECESSARY is TOO MUCH!

Others are persuaded by the claims of aftermarket manufacturers that their filters filter dirt "better than any other filter on the market." Sounds very enticing. To small timers like you and me, spending $1500 to test a filter sounds like a lot. But if you were a filter manufacturer and you believed your filter could filter dirt better than any other media on the market, wouldn't you want to prove it? ...

Now I am not saying that ALL aftermarket filters are useless. A paper filter does not do well if directly wetted or muddy. It may collapse. This is why many off-road filters are foam. It is a compromise between filtering efficiency and protection from a collapsed filter. Now how many of our vehicles collapse their filters from mud and water? However, if a filter is using "better airflow" as their marketing tool, remember this....Does it flow better? At very high airflow volumes, probably. BUT, Our vehicles CAN'T flow that much air unless super-modified, so what is the point? The stock filter will flow MORE THAN ENOUGH AIR to give you ALL THE HORSEPOWER the engine has to give. And this remains true until the filter is dirty enough to trip the air filter life indicator. At that point performance will decline somewhat. Replace the filter and get on with it.

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.