K&N vs. paper air filters

[Speed_Racer]

Wow, that was epic.

I agree. Who knew?

I'm afraid of posting my decision when I go to the autoparts store tomorrow for fear of starting it again.

[Rupert]

I've seen K&N debates before, but none where everyone was so pissy. It's another one of those things where there's not enough information available to make one side obviously right, and there's also a lot of misinformation out there. Like the oil change/type/etc. debate.

[S204STi]

I've seen K&N debates before, but none where everyone was so pissy. It's another one of those things where there's not enough information available to make one side obviously right, and there's also a lot of misinformation out there. Like the oil change/type/etc. debate.

It would have been a fine debate if Nick didn't have to be such a troll about it.

Like I said on page one, it's an emotional decision more than anything.

[Northlands]

Well, this is enough for me to consider putting the paper filter back in. I just liked the sound the K&N made. I don't really feel any increase in the car. I really don't like the idea of any of that oil making it in any further than staying on the filter itself. Kind of defeats the purpose of having a filter to begin with. Me and my foolish spending.. 

[GoCougs]

I've seen K&N debates before, but none where everyone was so pissy. It's another one of those things where there's not enough information available to make one side obviously right, and there's also a lot of misinformation out there. Like the oil change/type/etc. debate.

There's plenty of info to make it a black and white issue (as all issues are): works for looks/sound, doesn't work for power/mpg...

[giant_mtb]

Well, this is enough for me to consider putting the paper filter back in. I just liked the sound the K&N made. I don't really feel any increase in the car. I really don't like the idea of any of that oil making it in any further than staying on the filter itself. Kind of defeats the purpose of having a filter to begin with. Me and my foolish spending.. 

If you want a cool sound, cut a (larger) hole in your air intake box and use a paper filter.  Better effect, and free.

[Rupert]

It would have been a fine debate if Nick didn't have to be such a troll about it.

Like I said on page one, it's an emotional decision more than anything.

You guys were all dicks.

[S204STi]

You guys were all dicks.

Yeah you're right, I should have let him walk all over me with his incredibly strong argument.

If all someone can say is "Ju dun know anyting!  I R smartest!" as they throw a fit over something as trivial as an air filter then they are going to get pounced on.

Seriously, Nick, do you have K&N stock or something?  I still can't wrap my head around how you would take such a vested interest in defending them.

[r0tor]

Damn, this has been an entertaining thread to read today...when I could.  I couldn't reply in any detail because for once we actually got busy.

To rehash some comments here...indeed, it only take a few minutes to clean the MAF sensor.  Logically though, you should ask why you constantly have to clean it with K&N, not that it is easy so it isn't a big deal.  The reason for oil with K&N is to stop dirt from going any further than the filter.  Ask yourself, why you do not need to do this with a paper filter. 

If an air cleaner system claims less restriction (air flow) it logically can only achieve this one way...by opening up the pores to allow more air through.

Then there is the oil bath itself. Since it has been determined that the MAF will need to be cleaned, the next question is how soon?  If you install a freshly cleaned and oiled filter and oil comes off the filter and contacts the MAF sensor after driving the vehicle your performance will suffer.  If nothing else that small amount of oil is collecting on the platinum grid/wire and allow dirt to collect that much sooner and that much thicker which would insulate the sensor and change its readings to the PCM.

As I hinted, it isn't enough to take a manufacturer for their word.  If they claim something always ask why and how.  Forget bias as to why.  Ask instead why and how does the filter allow more air flow and how does that affect components downstream.

Couple points here...

- MAFs should be cleaned once every year or two regardless as no matter what filter you have on, it still gets dirty no matter what.
- I clean my K&N once a year... and also take the 2 minutes to clean the maf
- Proper "recharging" of a K&N filter should utilize the absolute least amount of oil you can spray on while getting full coverage.  If the filter is soaked you did it wrong.  If you put a piece of newspaper behind the filter, blow some shop air through the filter, and oil gets on the newspaper - you also did it wrong.

Pressure drop across a filter is also not proportional to the ability to to filter either.  A really awesome filter can have a low dp and also a high level of filtration if it is designed correctly.  You can achieve this by proper material selection, careful attention to the pleat design and density of the filter, and also how it manages airflow entering and exiting the filter (in a cone type filter).

[r0tor]

And is your MAF before or after the PCV inlet?

Mazda doesn't actually use a PCV valve in the rotary - just basically a vent from the crankcase.  In my year RX8 its located near the throttle body.  Enough oil collected (or was also burped) into it that oil coated and overflowed the accordion style rubber air inlet tube and oil was laying in my intake box... no real bad effect occurred except a slimy filter and intake

[JWC]

I made it clear that a K&N should be properly maintained.  While I've read recommendations to clean an MAF sensor with every filter change, I've also have cars out that that pass MAF tests with over 150,000 and the MAF has never been cleaned. 

I've also seen demos of air filters at auto shows and it is eye opening how much dirt gets pass a K&N.

[S204STi]

Couple points here...

- MAFs should be cleaned once every year or two regardless as no matter what filter you have on, it still gets dirty no matter what.
- I clean my K&N once a year... and also take the 2 minutes to clean the maf
- Proper "recharging" of a K&N filter should utilize the absolute least amount of oil you can spray on while getting full coverage.  If the filter is soaked you did it wrong.  If you put a piece of newspaper behind the filter, blow some shop air through the filter, and oil gets on the newspaper - you also did it wrong.

Pressure drop across a filter is also not proportional to the ability to to filter either.  A really awesome filter can have a low dp and also a high level of filtration if it is designed correctly.  You can achieve this by proper material selection, careful attention to the pleat design and density of the filter, and also how it manages airflow entering and exiting the filter (in a cone type filter).

I agree that the MAF should be maintained, as long as the manufacturer is OK with you spraying it with chemicals.  I also agree with correct filter service being hugely important.  However, I still reject the idea of using something that can contaminate the MAF sensor in the first place.  Paper filters simply do not run that risk, and as JWC pointed out most vehicles go their entire lives without a MAF cleaning, with zero driveability concerns.  Additionally, more dirt let through outweighs even a small gain in power, no matter how small the amount of dirt or how big the power gain (realizing here that an air filter alone won't give you huge results).

Mazda doesn't actually use a PCV valve in the rotary - just basically a vent from the crankcase.  In my year RX8 its located near the throttle body.  Enough oil collected (or was also burped) into it that oil coated and overflowed the accordion style rubber air inlet tube and oil was laying in my intake box... no real bad effect occurred except a slimy filter and intake

That's odd that the Mazda allows oil to drip into the air box.  But my point is not that I am concerned about oil entering my intake; clearly the PCV system takes care of that for me.  My concern is instead that oil should enter the airstream upstream of the MAF sensor. But the MAF sensor is not in line with that oil source normally, hence is never contaminated on most vehicles. 

MAF sensors can also be contaminated by poorly fitted paper filters, torn filters, filters eaten by rodents, or those that are clogged and end up deforming due to vacuum and allowing dirt through.  There is no perfect solution, but the best is a properly fitted paper filter as far as I can tell.  When someone comes up with a filter and works as well, is dry, and also flows better I will give it a shot.  I hear Amsoil came up with just such a design. 

[r0tor]

AEM has a "dry Flow" filter for a few years now.  For the record, when I replaced my stock airfilter with the K&N after a year of use, my MAF was jut a dirty -shrug-

All the tests linked on page 1 show the filtering efficiency being 96-97% vs 98-99%.  The amount of dirt passed is only significant if you scale a graph creatively.

[Byteme]

AEM has a "dry Flow" filter for a few years now.  For the record, when I replaced my stock airfilter with the K&N after a year of use, my MAF was jut a dirty -shrug-

All the tests linked on page 1 show the filtering efficiency being 96-97% vs 98-99%.  The amount of dirt passed is only significant if you scale a graph creatively.

Then it boils down to do you want a filter that allows double the dirt to pass to the engine, oils the MAF sensor, and requires periodic maintenance involving time and additional expense for a gain of half a dozen HP at or near the redline.  Or do you want the convenience of a disposable filter and double the filter effectiveness at the expense of half a dozen HP at or near the redline.

As has been pointed out it's largly a personal choice.  I'll opt for the paper filter.

I think what R-inge and others, including myself, have been pointing out is the K&N's are not the wonder filter that does everything well.  They are a trade off, like just about every thing else in life.  Hence the challenge to their claims which only point out the virtures.

[r0tor]

Then it boils down to do you want a filter that allows double the dirt to pass to the engine,

Again a reality check.... "double" is creative math and double of next to nothing is still next to nothing.  Its like telling your child who got a 96% on their math test that they did "twice as bad" as a classmate who got a 98% on the test because they got 2 questions wrong on a 50 question test while the other person got 1 question wrong.  In reality, they came within 2% of each other in getting things right.

In the real world with changing your paper filer once a year, your lucky to have .5 pounds of dirt caught in the worst case (think about the weight of a dirty filter vs a new one...).  That means it had to filer .505 pounds of dirt, it caught 99% or .5 pounds, and left through 1% or .005 pounds.  If you had a K&N filter, it would have caught .49 pounds of stuff and let through .015 pound.

The real difference is a hundredth of a pound of dirt!

[NomisR]

Again a reality check.... "double" is creative math and double of next to nothing is still next to nothing.  Its like telling your child who got a 96% on their math test that they did "twice as bad" as a classmate who got a 98% on the test because they got 2 questions wrong on a 50 question test while the other person got 1 question wrong.  In reality, they came within 2% of each other in getting things right.

In the real world with changing your paper filer once a year, your lucky to have .5 pounds of dirt caught in the worst case (think about the weight of a dirty filter vs a new one...).  That means it had to filer .505 pounds of dirt, it caught 99% or .5 pounds, and left through 1% or .005 pounds.  If you had a K&N filter, it would have caught .49 pounds of stuff and let through .015 pound.

The real difference is a hundredth of a pound of dirt!

Well, a considering how hot the rotary runs, how much of that dirt would be burned off anyways.  As long as the big particles are not going through, I don't see it being an issue especially with the oil change requirements with the Wankels. 

[Rupert]

Screw it, stick with ram pipes.

[S204STi]

Screw it, stick with ram pipes.

Velocity stacks?  Yeah, I'm ok with that.

[Speed_Racer]

AEM has a "dry Flow" filter for a few years now. 

That's what I'm going to be getting. I don't have the original air filter box (previous owner discarded it I guess), so it has to be a drop-in filter of some sort. I've read really good things about the DryFlow, it's no more expensive than a K&N, reusable, dry, and avoids the K&N conflict. Haha.

[Secret Chimp]

The K&N filter oil is really, really sticky. I was re-oiling mine in a stainless steel kitchen sink, and I had to use some of the cleaner fluid to get it to come off of the metal. It's not like cooking oil that would come flying off in half a mile.

[ChrisV]

What I have read about the subject is that automakers spend quite a bit of money on intake filter/box/tract design, to take advantage of the pulsing effect of the intake charge WRT to the firing of the cylinders. This advantage is along the lines of throttle response, and otherwise maximizing performance.

I havne't read teh entire thread, but here's my take on this statment.

If this was true, and they spent gobs of money maximizing performance of the air intake, then why do they NEVER maximize performance in any other part? If your statement was true, then how much power a stock engine makes is the total amount of power it can EVER make, and no one ever ported and polished their way to improved hp. Because those factory engineers spent way more money and are way more educated than any hot rodder.

No, manufacturers maximise the compromise of cost, NVH, and waranteeability.

[GoCougs]

I havne't read teh entire thread, but here's my take on this statment.

If this was true, and they spent gobs of money maximizing performance of the air intake, then why do they NEVER maximize performance in any other part? If your statement was true, then how much power a stock engine makes is the total amount of power it can EVER make, and no one ever ported and polished their way to improved hp. Because those factory engineers spent way more money and are way more educated than any hot rodder.

No, manufacturers maximise the compromise of cost, NVH, and waranteeability.

But the the impetus still falls on K&N and its defenders to explain the "compromise" behind the design/specification of an air filter that would rob and engine of power and MPG.

[AutobahnSHO]

No, manufacturers maximise the compromise of cost, NVH, and waranteeability.

+1
Or tuners wouldn't exist and aftermarket or performance parts wouldn't exist.

(But I will probably never even try "cleanable" filters..)

[ChrisV]

I used K&N on a number of my carburated cars, especially when the rest of the engine is built up, as they do flow more air for longer periods of time. I've known people that have had problems on MAF equipped cars with oil contamination, and others that have never had MAF contamination with K&Ns, so it may be a case of proper vs improper oiling of them. Personally, on a MAF equipped street car, I'd rather replace paper filters more often than take the chance that I put a little too much oil on one time and mess up the MAF.

As an aside, I've used a similar filtration system on paint booths before, where the exhaust air is blown across a water trough, and the paint particls stick to the water surface while teh air itself bounces off and continues. It's more effective than just a filter. Supposedly, the K&N works similarly. The air doesn't go straight through, it tends to bounce off the oil coated fibers, where the particulate sticks and the air continues on. Unlike paper filters, where the size of the hole is what traps the particulate, so the voids have to be smaller and slightly more restrictive, the oil in the K&N does the trapping, so the voids in the filter can be larger and less restrictive to the air without having to worry about larger particulate getting through.

[NomisR]

I used K&N on a number of my carburated cars, especially when the rest of the engine is built up, as they do flow more air for longer periods of time. I've known people that have had problems on MAF equipped cars with oil contamination, and others that have never had MAF contamination with K&Ns, so it may be a case of proper vs improper oiling of them. Personally, on a MAF equipped street car, I'd rather replace paper filters more often than take the chance that I put a little too much oil on one time and mess up the MAF.

As an aside, I've used a similar filtration system on paint booths before, where the exhaust air is blown across a water trough, and the paint particls stick to the water surface while teh air itself bounces off and continues. It's more effective than just a filter. Supposedly, the K&N works similarly. The air doesn't go straight through, it tends to bounce off the oil coated fibers, where the particulate sticks and the air continues on. Unlike paper filters, where the size of the hole is what traps the particulate, so the voids have to be smaller and slightly more restrictive, the oil in the K&N does the trapping, so the voids in the filter can be larger and less restrictive to the air without having to worry about larger particulate getting through.

So in conclusion, the K&N filters should work theoretically without causing additional harm to the engine but only if it is used properly.  And the reason why manufacturers don't use them is because they have to base their warranty of proper usage of the item which is too big of a risk to them.  Cheaper and safer with paper.

[S204STi]

So in conclusion, the K&N filters should work theoretically without causing additional harm to the engine but only if it is used properly.  And the reason why manufacturers don't use them is because they have to base their warranty of proper usage of the item which is too big of a risk to them.  Cheaper and safer with paper.

Certainly a plausible summary.

I tend to agree with ChrisV that using them on a carbeurated car probably isn't a problem at all.

[Laconian]

How difficult is it to properly inspect and clean my MAF sensor? Do I have to take it apart?

[ChrisV]

How difficult is it to properly inspect and clean my MAF sensor? Do I have to take it apart?

Kind of. Some cars it's easy to get the sensor out, and some cars you can do it after just taking the airbox and tube off...



Here's the hard way: http://www.louv.tv/cars/m5/MAF/

Here's the easy way: http://www.bimmerboard.com/forums/posts/343329

[r0tor]

mines just in with 2 phillips head screws... disconnect the plug, unscrew the 2 screws, and out it pops

[Secret Chimp]

How difficult is it to properly inspect and clean my MAF sensor? Do I have to take it apart?

On our cars, you just unplug it and remove it from the elbow and the crossover tube. There's kind of a "bullet" shape in the center; on the side that faces towards the front of the car you can see the MAF wires.