K&N airfilter/gas milage

[Guest md80man]

Has anybody figured out how much better my gasmilage will get by replacing the stock airfilter with a K&N air filter? my job is forcing me to drive 2,000 extra miles a month over this winter, and I was wondering how long til the $45.- is recouped Thank you in advance.

Edited September 7, 2005 by md80man

[Pezzy]

I believe it's about 1 mpg, if that...

[mws]

Or you can do like K&N's marketing group and let the stock paper filter get REALLY REALLY dirty and so plugged up the engine will barely run before checking the mpg, and then switch to a perfectly clean K&N and compare! WOO-HOO! Look at the huge improvement!

 

Bottom line: The OBJECTIVE tests I've seen and performed (excluding injected diesels, which are a different critter) to compare clean paper to clean K&N show little to no difference to mpg while at cruise - and sometimes a fresh paper filter appears better - so I suspect it is more test error than any real benefit. Yes, K&N's do flow better at very high flow rates (unfortunately, more air AND lots more dirt) so they should result in better mpg at full throttle, but I assume you won't be doing much of that if you are striving for maximum economy... At cruise rpm, the paper filters can flow more than enough air with minimal restriction.

 

So you will will likely never recoup the difference while commuting this winter if compared to a paper filter changed regularly. Over 100K miles, you will recover the investment due to not buying new paper filters. Over 200K miles, it starts going the other way due to the cost to rebuild the engine due to all the dirt passing through the K&N and wearing the cylinder walls and rings...

[88pathoffroad]

mws: I've had my K&N on for years now and the TBI's still shiny and sparkling clean as the day it was polished. How much dirt again?

[Simon]

Agreed. My K&N has been in for 4 years plus, everything past the filter on the intake tube is clean as a whistle.

[mws]

My experience:

Buddy's dirt bike (tweaked out XR-350) performance slowly degraded over a season until it ran like crap. Lots of digging revealed the needle and needle jet were severely worn. Wondering why, we asked around, and the common question back was "are you using a K&N?". Many had seen the same thing happen and advised against using K&N's in dirt bikes if extended engine life was desired.

 

Being skeptics at heart and engineers by training, we conducted our own experiment after installing a new jet and needle in to fix the problem. We smeared a thin film of white grease all over the inside of the airbox and intake tract beyond the filter and rode for 100 miles with K&N filter, and then cleaned and repeated using a UniFilter (oiled foam). All on the same weekend. 100 miles on day one, 100 miles on day 2, riding the same trails. The sealing surface on both filters was well greased and the filters were inspected for tears. I am pretty sure they were as good as can be expected. Always a risk we missed something, but I know we were more meticulous than the usual user...

 

The grease was noticeably (WAY noticeably) dirtier with the K&N than with Uni. It was a very fine dust that just left the grease dirty looking (tan) and only mildly gritty feeling, but it was there. There were not paper elements available for this bike to compare to, but other tests I've seen showed quality paper elements were even more efficient at stopping fine dust than Uni's.

I always encourage others to duplicate the test and make their own conclusions. Use grease to capture the dust, and use a very thin film to avoid ingesting it. The best place to put "sampling" grease is the outside perimeter of bends where the dust tends to be flung out of the air stream.

 

I will point out that our local dirt is mostly decomposed granite and other volcanic stuff so it is full of silica and much more abrasive than most so any wear will occur more rapidly. I would imagine that if your resident dirt is softer stuff with no silica, the risk of premature wear goes way down and wouldn't pose a problem for many more miles. If your soil is made up of really soft minerals, it probably presents zero risk. Heck, if you rode in graphite it may reduce wear! We are worst case so I am sensitive to the issue.

[Mr. Pickles]

Aren't K&N's supposed to filter cleaner when mildly dirty than when brand new? Anyways, I've had mine for 3 years with no issues, just a very clean airbox (drop in filter).

[MaritimeMan]

Was the K&N also oiled? I know the cone I dropped in my pathy has done very well without a single problem. I've even cleaned it one and re-oiled it.

[gabod7]

Was the K&N also oiled? I know the cone I dropped in my pathy has done very well without a single problem. I've even cleaned it one and re-oiled it.

thats all you gotta do and they will last for a very long time.

[mws]

Yes, the filter had been cleaned with K&N cleaner and oiled with K&N exactly per their instructions.

And once the large pores in the gauze are filled with larger particles of dirt, then it will stop the finer stuff. Of course, once the pores are clogged with dirt, then the flow rate plummets back down to about the same as any other filter.

 

And I am not surprised that there is no apparent damage after only 3 years. My concern is all the fine dust passing thru the combustion chamber will result in cylinder wall and ring wear over the long term. I would estimate it will take 50K to 200K+ (depending on the hardness/abrasiveness of the dirt going through) for the wear to become significant enough to affect compression or oil consumption enough for you to notice. The rings will continue to seal quite well even after a few thousandths of wear.

 

The relatively soft aluminum and brass of the needle jet in the bike wore about .010-.020 in 2 years riding - about 2K miles. Since the cylinders are iron, they wear much slower.

 

Don't get me wrong, I have and will continue to run K&N's in some of my vehicles when I want that last 1-2% of power and do not plan to keep the vehicle long enough to care about the wear. That's the moral of the story - use them with understanding of the benefits AND risks.

 

My track bikes are either no element or usually K&N's. Similar philosophy as to why you see many vehicles raced with K&N's - since the engines in race vehicles are rebuilt regularly, engineers care less about the accelerated wear and more about that touch more power at the race start. My 240SX had a K&N as it was street driven only and I knew we would be not be keeping it for more than 80K miles or so.

But because of our abrasive dust, ALL of my dirtbikes get oiled foam only.

Our BMW gets top quality OEM paper as we plan to drive it for at least 300K+ miles before rebuilding.

The tow van will use paper for day to day use, K&N when towing over the sierras.

The current engine in my pathy is already well worn and borderline in need of a rebuild, so I will use paper to minimize any additional wear. When I rebuild it, I will use only paper in the dirt. But since the rebuild will probably see see only 100K miles before the rest of the truck crumbles to dust, I will probably use K&N on the street where it needs that last 1-2% of power!

[thunderca]

Has anybody figured out how much better my gasmilage will get by replacing the stock airfilter with a K&N air filter? my job is forcing me to drive 2,000 extra miles a month over this winter, and I was wondering how long til the $45.- is recouped Thank you in advance.

I don't notice gain in my gasmilage after getting a K&N filter on.

[glenn]

I added JWT pop charger [same thing as K&N cone] and put on dynomax turbo exhaust. Together I got about 10-15% increase in MPG.

[revgolem]

I really hate jumping in the middle of this long running debate (both on and off these forums)... but I do have an interesting point. Dodge for a long time was having to replace a LOT of engines under warranty not too long ago. When research was done into the cause of all the failures and problems, they were directly linked to K&N filters. As a result, if you put a K&N filter on a Dodge, you immediatly void the warranty completely.

 

But it's like anything, some have luck with it some don't. Just like Stopleak, Freeze12, and remanufactured parts.

 

Personally though, like mws said, once the filter is dirty enough to actually clean the air (which is a funky concept to for me anyway) there's not much of an advantage... and oil from the filter does get pulled into the intake. But that's just this mechanic's humble opinion.