sasilverbullet

Not to start a FEELINGS war here, but I ran the K&N in my 87 turbo for years and then was convinced (i may have been drunk... <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" /> ) to go back to paper.

QUESTION: Can anyone quote me some FACTS about the paper vs. K&N dilemma? Please no 'facts' stated by K&N, I don't trust them. Any independent studies?

Thanks everyone!

smokey

I don't have any facts, but I've gone back to paper after rebuilding the engine on my 951. My reasoning is that anything that provides less restriction is also going work less effectively as a filter, and I want to reduce the possibility of cylinder scoring.

AMCPILOT

Mike,

You know my opinion ... the Factory one is overall a better way to go ... I think I posted an article in the May or June Longhorn Region "Roundup" newsletter (www.longhornpca.org) on this. Check it out.
By the way, if filters like K&N are so great, why don't manufacturers adopt something similar. Could be warranty, liability etc... or it could just be that they don't do all the things they claim to do. Besides, most of us drive our cars in the real world (dusty, dirty areas of all kinds). I guess the real question is where/how you intend to use your car and don't believe all the marketing hype you hear in the search for just a few more HP. I know others will have their own opinions, but this is food for thought. <img src="graemlins/nono.gif" border="0" alt="[nono]" />

Here is the article I ran:
Are "Performance" Air Filters a
Good Idea?

The following information was taken from a posting by Jim Conforti (AKA the Land Shark). Jim is a well known tuner in BMW circles. His web site is the Bonneville Motor Werks. The testing was done on a BMW air filter but the concepts should apply to all manufacturers.

First, a "prologue". 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"). OK, with that in mind, onward.
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 thru the TEST filter and is then captured on the analysis membrane we can calculate the efficiency of the TEST filter in Question. First, the filters:
1. BMW Stock Filter, Eff. Area of Media: 8.4 sq ft.
2. 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 air box. 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 thru 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.

smokey

Thank you AMCPILOT. My intuition is now backed by science. When I checked my K&N after half a season of track, I couldn't believe how clogged it was. When we rebuilt the engine, we had to rebore and go oversize due to cylinder scoring. Probably unrelated, but I'm paper forever, and I'm changing the filter every season. Keeping dust out of the engine makes sense to me, which is why we have air filters.

Levish

I have some quick questions

was the K&N airfilter oiled? they usually filter dirt out more effectively if they are (and not over oiled)

there is a even higer flowing foam based filter (ITG for example) this is also usually oiled and cleaned as needed. I am unsure as to weather it would be better or worse than the K&N or Paper filter in comparison though

RAPID944

Read this -&gt; <a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic&f=14&t=002077&p=" target="_blank">928 board</a>
<img src="confused.gif" border="0">

PorscheG96

[quote]Originally posted by AMCPILOT:
<strong>By the way, if filters like K&N are so great, why don't manufacturers adopt something similar. Could be warranty, liability etc... or it could just be that they don't do all the things they claim to do</strong><hr></blockquote>
Because modern car manufacturers are ruled by accountants and auditors with iron fists...K&N filters would be a huge expense over paper, in addition to one less replacement part they could charge customers for, and the service intervals of the K&N are more frequent than replacement of a paper one [if you do it right] which is a hassle for the consumer.

BTW I've had a K&N in my 944 for over three years and a K&N in my 968 for about a year and neither has experienced any problems because of it...the 968 uses a MAF wire and when I looked at it while replacing the radiator it appeared new. The guys in the 928 thread are correct, you've gotta let the things DRY before putting them back in the car.

Danno

"My reasoning is that anything that provides less restriction is also going work less effectively as a filter, and I want to reduce the possibility of cylinder scoring. "

You have to take into account surface-area. If you put in two stock filters into a double-sided airbox, you'll have less restriction over all, even though each filter is just as hard to get through as before. That's how a K&N cone filter works, it doubles the surface area of the filter compared to the stock one. But each individual square-inch may have just as much, if not more restriction than the stock filter.

The other variable that's been left out in a lot of studies is proper maintenance of the K&N filter. At what intervals were the filters cleaned? What were their conditions at the end? I think K&N's assertion of 30K-miles is a bit optimistic. I clean and re-oil mine at every other oil-change.

sasilverbullet

See, this is why I'm sooooo confused <img src="graemlins/c.gif" border="0" alt="[ouch]" /> ! Joe, I don't doubt your facts, but like Danno said, "what was the condition of the K&N"?

Now I just talked to Kathy at Jones Auto Werks, and they said that they don't recommend them because sooo many people either OVER oil them, or don't oil them or clean them, I agree with that for the general public, but I'm not the general public.

Bottom line, IF (big if I know) you clean and oil a K&N air filter correctly, then will it 'suck' through bigger particles of gunk?

THAT's the question I need answered! Anybody have the answer?

<img src="graemlins/xyxwave.gif" border="0" alt="[bigbye]" />

atinybug

i read an article a few months ago comparing 4 major (japanese car) aftermarket filters

blitz
apexi
hks
k&n

apexi came out as the best filter and hks was worst. i cant seem to remember where i saw it or the url for it. they compared how much air was being let thru, and how much contaminants were let thru also. apexi came out on top for both, letting most air and least contaminants. i think k&n cleaned 2nd best, but blitz let more air thru than k&n. hks was by far the worst in everything

Levish

Id like to re-mention the ITG filter since flow is relevant to some, it outflowed the K&N rather consistantly so I would definately keep it in mind.

Outlaw952

One experiment on one type of filter (BMW) hardly makes for objective results. I would be more inclined to believe him if he did ten sets of each on 4 or 5 different types cars and results showed that K&N was lacking. Anyone with base knowledge of experiment design knows one data point by itself means nothing.

AMCPILOT

Hello,

Bottom line, of course is to each his own. For those who need to feel they are getting just that last 2 HP out of their engine and are actually willing to perform the proper maintenance, cleanings, and so forth, then fine. To me, I'd rather stay with what I know what works. The K&N that was on my car when I bought it was in such bad shape it actually collapsed in to the AFM when te engine was revved, not only choking flow, but I suspect sending pieces of the filter in with it. I was not impressed.
I suspect that if someone did a test of 100000000000 filters and was even able to repeat it successfully to show definitively that the K&N filters do not work as well as hyped, there would be those who would be unwilling to believe it, especially those who have either already bought one or those who sell them. I included an article of a test, and the 928 folks have first hand stories, yet there are still those who swear by them. I think Kathy is giving good advice as well ... she has had to repair a number of cars with problems over the last 20 years ... I wouldn't discount her opinion in the hopes that she may be wrong.
I also suspect that this is a topic that will not be concluded in an e-mail thread.

Mike, I think you would be better off considering why your compression is low (around the lower allowed limit according to the specs ... i.e. 6.5 bar) and how that affects your cars performance and not hope that a K&N filter will make a difference. I'd rather you saved your funds towards fixing what needs attention than putting it into something you will be disappointed in. IMHO.

Here is another article ... more FOod for thought.

K&N Air Filter Testing Don Pavlik 2000

Talk about modifying cars and eventually someone will mention a high flow air filter of some sort or another. I purchased a K&N air filter since I figured my S4 could use all the fresh air the turbos could inhale. But, I wondered if a filter actually made any difference. Ahhh, one of my favorite things: more testing!

I had, in my possession, a fairly accurate airflow measuring device--namely--the mass airflow sensor that the engine computer uses to measure incoming air. And, the means to read and capture said information via VWTool. While I was at it I stuck my GTech on the windshield to capture HP numbers. The numbers were meaningless since I was doing rolling starts. Oh well. I fired up my laptop and 1.5 hours later I had plenty of data to sift through.

For my testing I did 5 - 2nd gear runs with each filter. For each run, I steadied the car around 1200 rpm in 2nd gear then applied full throttle until around 7000 rpm. I chose this method to eliminate shifting and to keep the runs as consistent as possible. All runs were eastbound with the return westbound trip to let the intercooler cool off. The stock filter has 6000 miles of service under it's belt, the K&N was fresh out of the box.

I was surprised. The mass airflow sensor didn't measure one bit of difference between the factory filter and the K&N filter. None, zero, zip, goose-egg. I didn't really expect huge gains but I did expect some difference! The airflow numbers from both filters were, for practical purposes, nearly identical. There were small variances here and there but the same type of variances existed between each group of runs on the same filter. As far as the airflow sensor was concerned nothing had changed. (see the large, slow loading graph below) My apologies for the different RPM scales on the graphs. Nothing I could do about it.


The graphs

Ohhh, I can hear it already... "you didn't measure any difference because you have that evil, restrictive factory airbox. Yup, that's your problem... you need one of those big cone filters so those turbos can really breathe deeply." Uhhh, I'm afraid not... you won't ever find one of those on my car. With the massive amount of underhood heat the S4 produces why would I want my engine ingesting power-robbing, super-heated air when nearly ambient temperature air is picked up by the snorkel behind the grill?

So what does all this tell me? At this point, unless someone can tell me why these results are invalid "me thinks" that popping in a high performance air filter in my S4 yields zero horsepower, zero improvement. Some would argue throttle response is more crisp. I don't feel it. If no extra air is making it's way into the engine it CAN'T be making any more power. No extra air, no extra fuel. No extra fuel, no extra power. All the high performance filter manufactures have graphs showing how their filter outperforms all the others.. under different conditions they probably do but my S4 does not have air filter induced asthma. I'm not suggesting that the K&N does not, under different conditions, flow more air just that in this particular case the air filter is not a restriction. I wish I had a stock filter with 20,000 miles on it to see how dirt effects its performance.

And finally, the filter did not change the sound of the turbo or intake noise

Levish

[quote]Originally posted by AMCPILOT:
<strong>Here is another article ... more FOod for thought.

K&N Air Filter Testing Don Pavlik 2000</strong><hr></blockquote>

This single article has caused me untold grief on the Audiworld forums, and despite me showing quite a few differential dyno's on exactly the same dyno/same car/same day of a few filters

a few things:

1. Measured with a Vag-com laptop through stock sensors (taking readings from a MAF essentially, not actually measuring the airflow, just sensor voltage)

2. Not measuring horspower before and after (not a dyno done just readings for a MAF)

3. Not taking into account that just airflow through the meter isn't the only way to produce power ... on turbo cars even at the same boost levels you can improve power (sometimes even lower levels)

Jaxon

Sounds like the K&N is a waste of time and money!
after reading that 928 post.

Stupid Question

What's involved in going back from K&N to PAPER?
Is the paper filter the same shape as the K&N?