What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

K&N Filter -- Thumb's Up? Or Thumb's Down?

jjhoneck

Well Known Member
I'm in the middle of my first condition inspection on my RV-8A, and just replaced the existing K&N air filter with a new one. I then made the mistake of posting a picture on Facebook.

Holy ****! Since posting that pic, I have been lambasted by several people who continue to tell me that K&N air filters let WAY too much dirt into the engine, and can significantly shorten the life of said engine.

This seems a bit odd, to me. I've used K&N filters on motorcycles and high performance cars for years, without trouble -- but none recently. Has something changed?

So....what's the group-think on this? Yay? Or Nay?
 
......along with the fact that the air ingested into an airplane engine is usually far away from the ground.
 
they are nuts

It seems the more mis informed someone is the more likely they are willing to share their ignorance. KN is a good filter, plus once you are above a few thousand feet the air is a lot cleaner than on the surface.
 
Something I'd worry about if I was based on a dirt field in the Sahara. Based on a paved strip or a grass strip? Not a concern, IMO.
 
Misinformed

I think most of people's negativity towards a K&N filter is derived from all of the Chinese copies that look like K&N's.

I've been using K&N filters for years on my aircraft, Harley's, and my Vette. With a good cleaning and recharge of the filter, they can't be beat. If the throat of your carb/intake is and remains clean, then I'd say it's doing its job.
 

Good Data. My professional knowledge in a paper element vs K&N comparison is decades old, but it is qualitatively the same. There is a standardized test for air filtration using official AC dust, so it is hard to compare quantitatively to the referenced data. Whether this specific test and data are important, is related to how much contamination is in the ambient air. Previous comments relative to aircraft application seem relevant.

Just my $.02
 
Wow -- that study is pretty telling.

So...what's the thinking on K&N competitors? Anyone recommend a drop-in replacement that's better?
 
Wow -- that study is pretty telling
Agreed - if you drive a GM Truck.

I am not sure it has any relevance if you fly an RV however :eek: Note they have ignored the "performance" implications of various filters, with a one off statement "The benefits of simply changing from a dirty filter, to a clean one, will give more benefit, than just changing from one filter style to another"

Most posts on this forum are about optimising performance e.g. ram air intakes. Little point in doing all this work and starving your engine of air to try and extract tiny dust particles that:
  1. Firstly won't be there whilst flying
  2. Secondly would probably just get sucked through and spat out of a Lycoming type engine anyway

Plenty of high performance aircraft run with no filter at all. I am not necessarily advocating that, but just we need to be careful comparing apples and oranges and all that ;)
 
Clean for five years

Clean, re-oil and reuse the first five years then replace. The reason you'll want to replace is because they shrink. I got seven years out of mine. The shrinking issue is in another thread.
 

I think it's a reasonable test, certainly the sort of thing more of us should do for ourselves, rather than rely on someone's marketing department for education.:rolleyes:

FWIW, I'm flying a K&N, but I've never thought of them as being a particularly effective filter. Nothing new here. I seem to recall magazine tests 30 years ago showing ordinary pleated paper to be superior to oiled gauze for catching small particle sizes. Lousy filter or not, it does a good job of stopping gravel and grit, bugs, FOD, and plastic bags. As noted in past posts, a K&N with enough media area is not necessarily more restrictive than an open intake.
 
Hold a K&N up to a light and you will quickly see why they are not restrictive, or really don't do a good job of filtering. There are some certified aircraft that use paper elements. Many of the newer types of automotive filters aren't made of paper so there's no reason to not try something better, as long as the alternate air source can bypass the filter. Which the silly carb heat design of the FAB air box can't get around. It really needs to be mounted on the plate inside the filter.
 
Silicon

I'm running a K&N on my Cozy and have had elevated silicon in my oil samples since first flight, not high but not what I'd like either. Dan H, you can see this in the two reports I sent you. I've looked for possible leaks but don't think I have any and have always suspected the K&N. I've tried extra oil on it and would replace it except I doubt it would improve anything and I don't think I could get any other product in there.
Second comment, I'd suggest there is dirt/dust/silicon in the air even at altitude. Certainly not what you'd suck up off the runway but I believe it's still there.
Tim
 
Last edited:
K & N Filter

I just purchased a 1999 RV 8, 0360 A1A, what filter number are you using on this standard RV 8 setup?
 
K&N filters are used on Detroit Diesel engines we have at work.
They don't last very long. They have published maintenance instructions. The elements should be inspected after cleaning; if you can see pinholes of light when you look thru the element, they are shot. Replace the element.
Also, they are made of cotton between stainless screens, so acid from any exhaust leaking into the intake will 'eat up' the cotton, and once again, the holes. These Detroits have crankcase evacuation, so naturally, the filters get 'ate up'.
I use K&Ns on our RV's, they ARE light and effective for an aircraft. I don't use them on my cars. If I planned to fly into some of those cool desert canyons and land on the dusty strips, I would consider an oiled media wrap over the K&N for some dust protection.
Bruce Finney has an old T-18 with a great big Buick 4Bbl air filter. Paper element and lots of surface area. That's one fast little O-290 hummer!
My T-18 has a Piper inlet box W/ air heat valve. The inlet scoop only has room for an oiled foam piece, similar to Brackett air filter media. When I have tried other media, the engine doesn't run right about 1700 RPM. Go figure?
Use what works. Check it often, fix as required.
 
I hated the shrinking K&N problem so much, i spent hours trying to find a simple replacement. Unfortunately, after several calls to Napa, Oreilly's and going to each individual manufacturer's website to find something close, i never was successful.

8.2 x 8.2 x 3.4 inches
 
Why would you replace a one year old K&N filter?:confused:

This is my first condition inspection, and the plane was built in 2003. I replaced it, on principle, because I had no idea how old it was.

I replaced all three tires with new, on the same principle. Sure, I could have flipped them around, and got another year, but they were probably the original tires.
 
Back
Top