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k & n filters

jeffcpajeffcpa Posts: 2
edited February 28 in Ford
i just purchased a new 98 f-150 4x4 with the 5.4
engine. i keep hearing about k & n aftermarket
filters. can someone tell me what kind of
performance gains this filter would give me?


  • AirwolfAirwolf Posts: 142
    Last entry got erased...
    K$N filters are GREAT! And worth the money. They increase HP by 5-15 depending on your vechicle (sometimes more but rarely) and increase fuel mileage by 1-2 miles a gallon.
    They are washable and reusable!
    Trouble is you usually have to order one. If you get one, let me know where, as I'm buying a 150 or 250 in the next few months.
  • jeffcpajeffcpa Posts: 2
    ryan, i appreciate your recommendation on the
    k & n filter. for that type of performance gains,
    its a no brainer on whether to get one or not.
    i just ordered one from my local napa dealer for
    about $54. if it will give me 1 to 2 mpg boost,
    it will pay for itself pretty quickly! i am getting about 14 mpg (i have about 1300 miles on
    the odometer), so it will be interesting to see
    what the filter will do for my mileage.
  • dunbartondunbarton Posts: 46
    Hey Guys,

    Don't want to sound stupid, but what KIND of filters are K & N: oil, air, fuel?

    Why are they so good vs others?

    About to make the plunge on a new EX cab full size and want it to last a long time. Dunbarton
  • cdeancdean Posts: 1,110

    do you have to buy the air filter from K & N or also a performance kit that goes with them. i've heard about great increases in power also, and i am looking at putting one on my '94 chevy 350 that has throttle body injection. but my air filter inlet is routed through a diverter plate that is designed to pull air intake from near the exhaust manifold when the truck is cold, that then switches to normal air intake from a cold box after warm up. it seems to me this diverter in the middle of the air intake is still going to limit the airflow, and it will still take more than just a different filter to increase performance. any info from anyone would be greatly appreciated.
  • cobra98cobra98 Posts: 75
    K & N Filters are air filters. Their claim is that they let a LOT more air through the element but less dirt. The more air, the better the air/fuel mixture, thus the more power and better mpg. My bet (no facts though, just hearsay), is that they don't offer nearly the HP increase that they claim. With that being said, I'm still going to put a K&N filter on my new Cobra and my '85 F150. I'm also going to use underdrive pulleys on the car, but they're probably also more hype than fact. But considering that neither item costs much, what the heck. I HOPE they help, but we'll see.

    Has anyone truely used them and believed that they helped? I know that a guy on "Coupes" used one and had his car dyno tested with different configurations and the K&N didn't help (mayber 2hp at a single rpm, but that's it).

    For more information, check out
  • AirwolfAirwolf Posts: 142
    They claim and increase of 3-5% (conservative) on HP increase based on engine type, driving conditions, etc. and 1-2 mpg better on fuel mileage. My 305HP Cobra will see a nice increase in both of these as that bugger sucks gas likes it's going out of style...could be how I drive it though... :)

    K&N makes air filters and oil filters. Their air filters are the most popular k&n item, as they have been out the longest. If I'm not mistaken, k&n oil filters have only been out a few years. As far as WHY they are better than other air filters are mainly in their construction. The materials they use are better than other filters mainly because:
    1) The filter breathes easier, thus increasing the air, thus increasing HP, mpg, etc. The filters are finer (less dirt and grime get through) yet designed to let more clean air pass through; and
    2) Better material means it lasts longer, and since it's washable and reusable, it pays for itself in no time. If you drive in normal conditions, it can go 50,000 miles before cleaning. And it STILL outperforms new factory filters when it's dirty!

    There are two basic type of k&n sir filters out there. The first is your basic $49.95 air filter. This is the most popular replacement performance air filter. Buy one and it's done. Forever! (Which is usually until your engine blows up or you sell the car) :)
    The other is an AirCharger. It's a complete replacment of the airfilter assembly to increase your horses up to 25% more (or something close to that). Very performance oriented and expensinve. Most models start above $200.
    I don't know about your vehicle in particular but I'm curious now to see how it would work. 4Wheel Warehouse sells a lot of K&N airchargers for trucks (usually more space under the hood for it) and I've read a lot of good things about them in Peterson's 4Wheel Magazine (best 4wheel mag IMHO).

    I just bought a new one for my '96 Cobra yesterday. It was one of those "I'll get to later" and never did. Now the next owner will be a happy camper when I sell it.

    HTH everyone,
  • cdeancdean Posts: 1,110
    thanks alot Ryan, i'm going to try to contact K&N, or maybe the nearest dealer, and get exact information. on the website, the example they sited was my exact truck, and they said there was a 10 hp increase, but they didn't say exactly if they put on the filter only, or the whole intake kit. i'll see if i can get to the bottom of this.

    thanks again

  • dunbartondunbarton Posts: 46
    With the purchase of a new full size picked on the near horizon, would the addition (replacement) of a K & N filter void any warranties that anyone knows of? I really wouldn't want to get into a hassle over a new car warranty.
  • dunbartondunbarton Posts: 46
    Disregard my question above. The K & N web site answered my question nicely: no, it does not.
  • lwflwf Posts: 223
    Call me a skeptic, but I don't believe you'll really increase the efficiency of your engine as much as stated above, if at all, merely by replacing a clean vehicle-manufacturer's air filter with a clean K&N. It seems to me, most of you are talking about a current MPG of about 14, and you expect to get 16, that is, a 14 percent improvement. Maybe if you're existing air filter is very heavily clogged those number might be reasonable, but then again you should expect that kind of improvement by replacing it with just a clean vehicle-manufacturer's air filter.

    If you have a fairly new ordinary air filter now and you were to simply remove it for about 100 miles of highway driving in a clean environment, I doubt very much if you would see any perceptable difference in efficiency. The K&N, no matter how good it's design, has to restrict more air flow than no filter at all, so if driving with no filter doesn't make a difference, how can the K&N cause an improvement?
  • AirwolfAirwolf Posts: 142
    The K&N website ( does a much better job of explaining than I can, but I'll try - briefly.
    A clean new air filter with your car is a standard make filter, usually extremely cheap in cost and make, does fine job for a few thousand files. The grit and grime eventually clog up the poorly made material.
    No filter is the worst you can have. The filter provides clean air to the engine. CLEAN air. No filter would allow everything that makes are dirty to enter the engine, and reduce your performance tremendously.
    K&N filters clean the air more thoroughly, and allow more CLEAN air to enter the engine. The surface area of most K&N filters is also greater than that of a conventional filter.
    IF you visit their site, you will have most, if not all, of your questions better answered.

    Good luck,
  • lwflwf Posts: 223
    Thanks for the response Ryan. I was afraid when I posted that last message, someone would misinterpret what I said to mean .... just run your engine from now one without an air filter..
    That's not what I intended, and I was very careful to indicate that kind of a test should be of short duration (about 100 miles) and I also included the phrase "in a clean environment". Personally, I'm a stong advocate of changing all filters frequently. But I think the air filters that the auto manufacturers make are so good at not providing air blockage that even if you were to run your engine without an air filter, the difference in MPG would be imperceptable to most drivers. The point I was trying to make was if you can't improve your vehicles MPG by running with no filter, how can you expect the K&N to be better than that? Buy the way, however, FYI there are some engines that never use an air filter. Aircraft engines, for instance ------ jets don't, of course, but neither do the ones that have pistons. And I've had quite a few outboard motors, and I've never seen an air filter on any of them, not even one that was 100HP. I've never had an I/O, so maybe someone will be able to tell me whether of not they have air filters. If any marine craft does, it would be an I/O because I'm pretty sure most of them have car engines. I suspect they don't, however. Sorry for getting off course, but I sort of got the impression that you belive that if one were to run an engine without an air filter, even for a short period of time, the engine would be ruined. I don't believe that either.

    I had been to the K&N web site before I made the last post, but I went there again at your suggestion. I'm afraid I still don't see anything they say that changes my opinion that I think it's a farce. I don't believe the air filters that Dodge, GM, Ford, etc. provide are products that are so inferior to the ones made by K&N that one could expect something like a 14 percent increase in fuel efficiency. If K&N will provide a money-back, no-questions-asked-if-not-satisfied guarantee, I'll take the time and trouble to try one. If that kind of a guarantee is there, I didn't see it.
  • cdeancdean Posts: 1,110
    i'm skeptical myself and i will ask plenty of questions before i spend $50.

    by the way, i have an I/O boat with ford 302. it does not have an aircleaner. on top of the carbuerator a metal filter looking can covers the intake to the carb. it is a spark arrestor and just prevents any back spark from setting the boat on fire. most small marine engines like mine don't have airfilters, because of the risk of fire.
  • lwflwf Posts: 223
    Thanks for the backup cdean regarding the air filter. I wasn't positive about I/Os not having an air filter, but I probably would have bet money on it, and I'm not really much of a gambler either. But I have been involved in discussions like this before, and I noticed that many people have almost a religious belief that every internal combustion engine in the world has to have an air filter. I guess that's based largely on personal experience with cars, trucks, garden tractors, lawn mowers and chain saws, all of which do have air filters because they operate in dirty environments, expecially the last three.
  • davepercdaveperc Posts: 76

    The K&N filter replacement only, probably is insignificant, as you suggest. The product that would provide improvement (that might be noticable) is the K&N intake housing replacement. Many engines have a large pressure drop due to the various cans, tubes and boxes that the air needs to pass through. I have an old BMW that has a K&N filter replacing the intake box and long coregated tube that goes to the front of the car. I have never had it stock but I do believe that getting rid of all that stuff does help. Remember that every elbow, bend and abnormal exit and enterance is a flow restriction. Take away all the crap and put a K&N filter with more surface area and you could find a benefit. Of course, this is assuming that the intake was a limiting component. The engine is a pump, with the intake, intake manifold, intake valves, exhaust valves and exhaust system being flow restrictions. If the exhaust (or other component) is the real breathing problem, then the intake mods won't help as much as it would otherwise. All the various restrictions add up. But generally speaking, the inexpensive mods that can boost performance are the intake and exhaust. Replace the exhaust when it is shot. Intake won't die, so if you want to try, you might get something, it is cheap. Then you can get real serious and have the head(s) ported and oversized valves installed.
  • lwflwf Posts: 223

    I understand the direction you're going in, but you'll have to admit that when all is said and done, these are nothing more than heuristic arguments. When K&N provides a money-back guarantee their products will do what it claims they should do, I'll buy them. Not before.

    As far as the air-intake system of an engine being a labyrinth of complex twists and turns, that's not my Ford F150. It's got a 3 1/2-inch duct that comes from the left wheel well through the air filter, and though another 3 1/2-in duct which makes one sweeping 90-degree bend into the engine. Doesn't look very complicated nor very restrictive to me.

    I do agree with you, however, that more could be done by auto manufacturers to improve the intake system on American-made pickups. In fact, I once posted something in this conference saying that it seemed to me that dual overhead cams and 4 valves per engine for all pickups would be a step in the right direction. I didn't get one response that agreed with me, but there were a number from others who definitely thought I was nuts.
  • stanfordstanford Posts: 606
    The main use of the K&N IMO is for increasing airflow. Their website has some good figures on this, including how to calculate air filter size for a given CFM need.

    This won't make a bit of difference to you unless you are in the habit of flowing more than, say, 450 CFM. Most people aren't. In a good car that sees WOT a lot, this would be a factor. Also if you were used to towing heavy loads (again at WOT). If you're just cruising around with 20-30% throttle max, I doubt you'd see anything.
  • lwflwf Posts: 223
    "dual overhead cams and 4 valves per engine for all pickups"

    I meant to say 4 valves per cylinder. Sorry about that.

    And I think stanford's point about wide open throttle and the fact that most of us seldom or ever do that is very relevant. Good point.
  • davepercdaveperc Posts: 76
    The expectations expressed in this thread are at the two extremes.

    The dramatic improvements stated at the beginning may be somewhat exadgerated. The amount of gain is greatly dependant on the vehicle in question. The claim by K&N of 5-15 hp is most likely the best case senario. That could have been a large displacement engine like a 454 with a huge maze of intake crap that would not let the engine breath at high air flow conditions. And likewise, the 1-2 mpg probably is a small displacement engine with the potential for good mileage but with a lot of restriction. May not have been the same engine for both. Prior to strict emmissions, things were simple (round air cleaner sitting on top with a hose to get cold air somewhere). When emmissions limits were imposed, manufacturers scrambled to comply and sacrificed alot. Since then they have designed the engines better and better, more efficient and free flowing, to get more performance out of the same displacement.

    The other extreme is that there is no improvement. That is not just, either. In an effort to increase the efficiency of an engine, each component of the system should be looked at. LWF, even that F150 of yours could be improved. Remember that the motive force is not very large. The engine is sucking the air. That means that atmospheric pressure (14.7 psia) is pushing the air into your engine, maximum assuming the cumbustion chamber is at a perfect vacuum (bad assumption). Thus chargers are effective at improving HP (10 psi boost can double flow). Using a previously stated value of 450 CFM, the air velocity through that 3.5" tube of yours is about 100 ft/s (rough #s). 3 ft of that hose, an air cleaner box,... all add restriction. Removing unneccesary restrictions will allow more airflow, and the carb/FI system senses more air flow and allows more fuel flow. More power, ONLY when the driver positions the throttle to allow more power. The throttle controls the engine by restricting this airflow. The mention of WOT being rare in your typical drive is true, but when discussing HP, this is a major factor. Notice that HP peaks are at the high RPM band, when the throttle is open.

    The real question is why are you interested in installing an performance improving component? For HP, WOT is the condition that you are trying to improve. If it is for mileage, these days I dought you will see it since the manufactures are all trying to get the best they can, where long ago, noone cared about milage. Today there is even a tax on "gas guzzlers", that the makers try to get out of. Fuel economy is improved by reducing energy used to do things other than move the vehicle down the road. The basics behind the intake system for fuel economy is restriction of the engine to rotate. At a constant throttle position, with airflow constant based on engine RPM (engine is a positive displacement pump) a given amount of power is lost due to the resistance to airflow. Reducing the resistance, will improve the mileage by reducing the amount of fuel/air mixture to maintain constant RPM. Even I, however, dought the 1-2 mpg figures seen above.

    Blah, blah, blah. I am sure I bored the hell out of all of you. Sorry didn't have time to spellcheck.

  • lwflwf Posts: 223
    Look, all I have is a 4.2 liter engine. Convert that number and you get 0.148 cu ft. I normally drive with the engine turning about 2000 RPM. Since it takes one rev to suck the air in and one to pump it out, that sounds like it takes 2 revs to "pump" (as Dave puts it) 0.148 cu ft of air. At 2000 RPM, I'm only "pumping" 148 CFM, a far cry from the wide-open-throttle 450 CFM that has been stated. For my engine to pump 450 CFM, it seems to me the engine would have to be turning at more than 6,000 RPM. Not me friend.

    And at 148 CFM, I believe the air flow in my 3 1/2 tube would be only about 37 ft/sec or about 25 MPH. Like I said, I'm a skeptic, and I just don't believe I have any significant air-flow loss at 25 MPH.

    But even though you sid you are in the middle Dave, your next-to-the-last sentence indicates you don't believe the 1-to-2 MPG gain claim either. So the bottom line is that you agree with me.

    As far as "why are you interested in installing a performance improving component?", I'm not. If I wanted more performance, I would have bought a bigger engine. If I wanted better fuel efficiency, I would have bought a smaller pickup with a smaller engine. I'm satisfied with what I have. One thing I can't understand is why people buy big trucks and afterwards want better efficiency or small trucks and later want more power, and really believe they can buy the same after-market device (a K&N air filter) that is capable of providing both. Makes no sense to me.
This discussion has been closed.