Anyone use K&N air filters - Subaru Newbie here

[the evil twin]

I can attest that K&N is only a "feel good" addition to any vehicle. Modifying one aspect of a complicated system will not yield any results. Put simply: If you take a garden hose with 3 valves on it and all 3 are 50% open then removing any 1 of them will not increase flow. I crude comparison, I know. However, there are other components that are "choke points" as well. Intake ducting, head flow (both intake and exhaust valve lift, duration, overlap, etc) porting, exhaust system, blah blah blah. Saves $$ ? Well, depends on what your time is worth to wash, dry and oil a filter as compared to tossing it in the trash.
Allows more particulate to pass? You betcha. If the filter fits in the OEM housing, it simply violates the laws of physics to claim otherwise. The only way to increase flow would be to increase the surface area (pleating) and K&N does not. Are their claims of efficiency true? Yes sir, but over the life of the filter before cleaning. Manipulated information.
Will you see performance increase? Sure. At WOT. How often do you put the "stupid" pedal on the floor on a dyno? Because that is the only place you will see an extra 8 HP. Do some research before you drink the Kool-aide.
Even with all that said, I have witnessed a vehicle that LOST top end HP with a K&N. Same motorcycle, same dyno, same tech, same day. It was an unmodified Honda CBR1000rr and it made better power with the OEM filter!
Do I use one? Yup. Well, a BMC filter which is similar. Although, only on the race bike which spends its life at nearly 13000 rpm. I wouldn't put one in any street vehicle if they were free.

[AWD Flyer]

While I agree you arent going to get a huge performance increase. It can save a few bucks over the course of the life of the car. Some cars I have owned the factory or aftermarket paper filters where $30 or more each. I would rather pay $70 for a K&N and 10$ for the cleaner/oil that will last quite a while. and save some cash in the long run, especially with the price of everything rising.

[foxrider68]

I quit using K&N filters once I held it up to the sunlight and saw tons of light making its way straight through. So then I took a rag and wiped deep up into the air intake and pulled it out and sure enough there was dirt. At that point I threw all my K&N filters and switched to Amsoil if its available otherwise I used paper filters.

[jlaudio_outback]

Originally Posted by the evil twin

I can attest that K&N is only a "feel good" addition to any vehicle. Modifying one aspect of a complicated system will not yield any results. Put simply: If you take a garden hose with 3 valves on it and all 3 are 50% open then removing any 1 of them will not increase flow. I crude comparison, I know. However, there are other components that are "choke points" as well. Intake ducting, head flow (both intake and exhaust valve lift, duration, overlap, etc) porting, exhaust system, blah blah blah. Saves $$ ? Well, depends on what your time is worth to wash, dry and oil a filter as compared to tossing it in the trash.
Allows more particulate to pass? You betcha. If the filter fits in the OEM housing, it simply violates the laws of physics to claim otherwise. The only way to increase flow would be to increase the surface area (pleating) and K&N does not. Are their claims of efficiency true? Yes sir, but over the life of the filter before cleaning. Manipulated information.
Will you see performance increase? Sure. At WOT. How often do you put the "stupid" pedal on the floor on a dyno? Because that is the only place you will see an extra 8 HP. Do some research before you drink the Kool-aide.
Even with all that said, I have witnessed a vehicle that LOST top end HP with a K&N. Same motorcycle, same dyno, same tech, same day. It was an unmodified Honda CBR1000rr and it made better power with the OEM filter!
Do I use one? Yup. Well, a BMC filter which is similar. Although, only on the race bike which spends its life at nearly 13000 rpm. I wouldn't put one in any street vehicle if they were free.

I would like to respectfully disagree. Let's say you are holding a hose to a shop vac. Hold up a piece of thick cut pile carpet to the hose. Now remove that and hold up a thin lace curtain. Regardless of other restrictions in the vacuum the curtain makes the vacuum pull more air because it is less restricted by the material its trying to pass air through. If its less restricted the motor will not have to work as hard to pull air in which will make it slightly more efficient.

As far as holding one up to the light goes, I can hold mine up to the light without more than a glow. If beams of light were coming through you had a damaged filter. I will always use K&N filters in my cars. I calculate MPGs on my car all the time and yes there is a difference. I get 1-2 MPG better gas mileage consistently.

[xvimbi]

I think the point that Looby and the evil twin are trying to make is that it is not the air filter that regulates the air flow but the throttle body butterfly. Only if the throttle requests more air than the air filter can deliver will you see a difference when changing the filter. They question that this will be the case often enough to justify changing from the stock filter. More drastic measures would have to be taken.

[jlaudio_outback]

I still disagree. Back to the vacuum reference. Regardless of if your vacuum is on low or high, restrictive material is still going to cause it to work harder and draw less air than it would through a less restrictive material.

[Looby]

Originally Posted by jlaudio_outback

Regardless of if your vacuum is on low or high, restrictive material is still
going to cause it to work harder and draw less air than it would through a
less restrictive material.

That analogy is seriously busted. Cruising at highway speed ain't even close
to your example of "pile carpet" vs "lace curtain" with the vacuum cleaner
sucking as hard as it can.

If you're not at WOT, the engine IS NOT sucking air as hard as it can. It's
only sucking enough air to generate the power required to maintain speed;
and at 80 mph, that's less than half of the design-maximum airflow -- far,
FAR less than half.

The PRIMARY restriction (intentionally!) limiting airflow is the throttlebody
butterfly -- controlled by your right foot. So, it doesn't matter at all whether
the filter is made of lace, or pile, or dirt-passing/gunk-shedding oiled foam,
or no filter at all. Whatever the case, the total airflow to the engine will be
EXACTLY the same -- because, in every case, the power needed to maintain
80 mph is EXACTLY the same. My friend Isaac says so.

...not just a good idea, IT'S THE LAW!

Looby

[jlaudio_outback]

Whether or not it is sucking as hard as it can, restriction from the filter will only make it suffer more. Whether a vacuum is on high or low you can still tell the difference in air flow between different material. Call K&N they will gladly discuss anything you want and provide you with any proof you want or need. I know what I am talking about and my 1-2mpg increase between a paper filter and a cotton one proves my theory. I never exceed 2500 RPM unless I'm on the highway. The last 2 times I checked my MPG they were 30 and 29. That's better than the 26-28 (at best) I was getting before. I will stand by K&N because I drive my cars 120 miles a day or more 365 days a year and I know there is a difference. I'm done arguing my point. We don't have to agree on everything. I don't like to argue so if anyone feels the need call K&N and argue with them. Let us know how that goes.

[xvimbi]

Don't you think that, if Subaru, or any other car manufacturer for that matter, could improve the mileage of their cars by 2 mpg simply by replacing the air filter that everybody would have K&N filters, or similar?

[jlaudio_outback]

No, because you sacrifice filtration for improved flow. A K&N filter will allow more dirt to enter the engine and no manufacture would allow that but if you don't mind cleaning your MAF sensor and running seafoam every filter recharge then its not that big of a deal. I recommend that you do those things every filter change anyway because every filter will allow some dirt in. More than you think too. manufactures constantly do things to rob a vehicle of power and mileage! With a little tuning from your ECU you can get more power or fuel economy. Sometimes even both. If K&N does nothing at all as you say then why do they sell so many and are completely willing to provide proof of improved efficiency for any vehicle to any customer?