anyone using a K & N Filter

Well my "stupid" questions are certainly giving you a platform to make K&N filters sound great.

If your Prius based business increases I want a cut....

 

My owner's manual states that the 2009 Prius engine air filter should be changed at 30,000 miles...page 11 on the internet copy(similar interval to the K&N). While I would never wait that long to change it, that extended change interval would negate much of the $ savings and environmental gains of reusables. Using anything other than a good paper filter seems wasteful.:car:

 

What am I missing here???

K&Ns forum statement says they neither advertise nor guarantee MPG gain on their web site, then somehow by quoting their web site citing increased power and acceleration, never mentioning anything to do with fuel mileage, you imply a conflict?

 

I ran a K&N for five years on my old Volvo Turbo wagon. When my Turbo seized at 247K miles I found the inlet impeller covered with an oily grime. When I replaced the Turbo I went back to a paper OEM filter.

The day before I clunkered it at 370K miles for my Prius, the guys at the garage I got it serviced were pulling parts off it. When they took off my Turbo hoses I saw that the inlet impeller was spotless.

It looked like it was brand new. 123K miles and not a spot of oil or dirt to be seen. That was all I needed to see to convince me that OEM paper is the way to go.

As tell other people, it's your car do as you please.

If I personally ever run across a used car with a K&N filter sticker on the air box cover or find one of their filters in the air box I'm walking on it.

 

^ That's precisely what I've seen on many cars, but in KN's defense perhaps the filters were over-oiled and placed in the intake box before dripping the excess. Maybe...

To each his own. KN filters are great, for some cars.

 

And how many cars 40 years ago had a MAF sensor?, 20 years ago there were still cars with carburetors, but they were getting rare.

 

It's nice that the K&N's are cleanable, but that's a catch-22. If there's alot of dirt in the air where you live, you don't want an oil-cloth filter because they don't filter as well.

The best comparison I know of (on the net) was done by a guy named Spicer a few years ago for some diesel-performance gearheads.

ISO 5011 Duramax Air Filter Test Report

You gain about 2 inches of water as less pressure drop (out of a total of 400 for an atmosphere) (a whopping 0.5%), but you pass 7.0 gms of dirt into your engine vs. 0.4 g for the stock paper filter. 17X more dirt...special calibrated test-dirt of course. Seems like the short end of the trade-off to me.

 

There is no doubt that they don't filter as well as a "paper" filter. Even K&N used to have some data on their website that showed that. A K&N is on the order of 96-98% efficient.

The question becomes, do they filter enough worse to make a difference. Do you feel lucky?

The can't improve MPG in a properly running, modern fuel injected car. The control system keeps the mixture correct over the range of restriction that you will get with a K&N or paper element. Any improvements noted are the result of poor testing or a good imagination.

Any reduction in restriction from a K&N element in a stock air box is overshadowed by the airbox and ducting restrictions and would only make a difference in power at full power if it did make a difference. How many Prius owners spend a lot of time at full throttle?

I just dug this up from from K&N's website

I have never seen an independent test of a K&N that got 99% efficiency, more like 96%-97% Paper filters normally get at least 99%. Doesn't sound like a big deal until you consider a 97% efficient filter is passing 3 times as much dirt as a 99% efficient filter.

 

:rockon: And, actually, Purolator and Wix were only 1/2 inch-H2O more restrictive than a K&N.

Also, if you look at the dust loading curves, the K&N becomes more restrictive than the better paper filters after not too much use.

 

Thanks for the reference! It substantiates my empirical opinion of K&N filters. Some years ago I purchased one for my 2002 Nissan Frontier pickup. Its gas mileage wasn't nearly what I thought it should be and my neighbor who owns a car repair shop recommended K&N.

When I was installing it I noticed that if you hold the filter up to a light source you can see pin-sized holes in the cotton matrix at the bends in the accordion folds. I wondered how effective an air filter can be when you can see daylight through it! But I used it anyway for about two-weeks and didn't measure any mileage gain. The pinholes started to worry me again so I removed the K&N and threw it on a shelf in the garage. If it doesn't improve mileage, why risk crudding up your engine?

After a couple of years of sitting on the shelf, I went back to it again after seeing a thread similar to this one on another group. The pinholes were still there, so I held the filter above a black surface and then sprinkled white talcum powder directly on the horizontal filter. Yup, some of the talc passed through the filter and ended up on the black surface with nothing but gravity doing the pulling. I suppose a well maintained and oiled K&N might work for its intended purpose on an engine, but I would always worry about the pinholes!