k & n filters

jeffcpajeffcpa Member Posts: 2
edited February 2014 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 Member 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 Member 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 Member 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 Member 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 Member Posts: 76
    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 www.knfilters.com
  • AirwolfAirwolf Member 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 Member 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 Member 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 Member Posts: 46
    Disregard my question above. The K & N web site answered my question nicely: no, it does not.
  • lwflwf Member 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 Member Posts: 142
    The K&N website (http://www.knfilters.com) 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 Member 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 Member 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 Member 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 Member 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 Member 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 Member 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 Member 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 Member 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 Member 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.
  • stanfordstanford Member Posts: 606
    Quite right. A shorthand formula would be:

    CFM = (CID * RPM * VE / 3464)

    VE = Volumetric Efficiency, btw. Assume 1 for ballpark estimates, although its probably a bit lower for a stock engine.

    Interestingly enough, this is a little on the low side. A 350 CID engine would require ~650 CFM at 6000 rpm by this calculation -- my 350 chevy (the only engine I have built that's been dyno tested) was drawing ~750-800 CFM at 6000 rpm (WOT). Admittedly, this was one peppy engine, but I don't believe VE was significantly over 1.0.

    As for your comment on power vs. efficiency, I believe you're referring to power vs. economy. If efficiency increases, both power and economy will generally go up (which is why a nice free flowing exhaust system is one of the best things you can do to your vehicle).

    Reducing paracitic losses can help your efficiency by 5-10%. A new air filter could help in two different ways:

    1) More maximum airflow. This may not be an
    issue depending on your engine -- it wouldn't
    help that 4.7 above for instance

    2) Less restrictive airflow. Your engine has to
    work to suck air into the system -- the less
    drag the air filter produces, the less power
    the engine is spending to 'breathe'. This is
    why 'ram air' systems that move air into the
    engine 'for free' can add 10-15 HP on a decent
    system... the engine doesn't have to spend so
    much power to suck the air in itself.
  • lwflwf Member Posts: 223
    By volumetric efficiency I presume you mean the ratio of the volume of air actually admitted to the displacement volume, and I obviously also assumed it was 1 in my calculation above. As you said, in reality it is probably less than 1; therefore, my estimates of 148 CFM and 37 ft/sec are, if anything, even higher than they really are. It seems to me that's an argument in favor of the premise that velocity of air flow for an engine's intake system isn't really all that high under normal operation; therefore, neither are the losses which, in turn, implies that the importance of replacing your vehicle's air filter with magical ones produced by an after-market manufacturer is blown way out of propotion to the benefit which can actually be achieved.

    Also, I stand corrected in that I used the word efficiency in place of economy. Thanks for pointing that out.
  • stanfordstanford Member Posts: 606
    Ah, but volume does not necessarily indicate efficiency. Just because your engine only draws 150 CFM at cruising speeds, I wouldn't assume that it draws it easily. If the engine is having to sacrifice 10-15 hp to suck the air through a dense filter at high speeds, it may still be costing 5 hp at slower speeds (where your engine is producing a lot less power anyway).

    Reducing this restriction can't help but increase the engine's power -- the question is whether or not that increase would be apparent. For some people, I'd say that it might not be. YMMV.
  • stevekstevek Member Posts: 362
    Wow!! that is a lot of tech talk. The replacement filter for my chevy truck cost almost $40. I got a K&N filter for $55, which do not need replacment. I usually keep my vehicles 10 years therefore the K&N filter saves me a lot of money. By the way the truck is not faster or gets better milage, but I did notice the engine runs a little quieter.
  • davepercdaveperc Member Posts: 76
    Stanford and Cdean,
    You guys were willing to put in more effort in explaining this than I was. Good work. I wasn't about to calculate the Re. But I would like to reiterate the point I tried to make yesterday.

    Why are you interested in this forum? To improve something? Performance or Economy? You have me confused. You were in the Nissan truck area complaining about the Frontier I4 engine's power, or lack of, as compared to the competitor's V6s. The I4 is much more economical, but the performance is not as good. Do remember that an I4 should be driven at higher rpms than the 2000 that you are used to. An I4 at 3000 is fine for normal cruising, and 4000 is not high for high demand situations. Like you said, when buying, you opt for one extreme, and accept the other. But, some people may be interested in more performance with no matter what they buy.

    At times when conditions are more demanding, higher rpm, an increase in performance may be achievable. Being familiar with the Ford I6, I know that your F150 is not a quick truck, especially driven no higher than 2000 rpm, or very economical. It is a good engine with a broad torque curve by design, great application for F150s. You own a truck that you don't drive aggressively (do you tow?), so a HP boost is not what you are looking for. Knowing that engine, it doesn't like high rpm anyways, and may not be a good cannidate for this mod.

    Say if your F150 had the 5 liter. And say you like to get up and go at a stop light, especially when that Ram sitting next to you is planning on cutting in front of you before the lanes merge. You step on it. Let that engine rev to 4000 before shifts. Not too unreasonable, for many, maybe not you. Well that air flow is now up to 350 cfm. Or take your truck, and put a big rig behind it and drive through the mountains. That 3 mile, steep grade could cause you to drop to 50 mph. But instead, you down shift, rpm to 3500, airflow is now 260 cfm. I could go on, my point being that noone is going to see performance improvements cruising at 2000 rpm. Cruising is light duty, even a nissan I4 can do that. Performance improvements are going to be noticed at demanding situations, like the examples stated above, not cruising or low rpm not demanding situations. Additionally, that 450 cfm stated above is not the whole story either. The flow rate that becomes highly restrictive is different for all different intakes. The head loss is a function of the velocity squared. Thus the velocity of the air is important.

    cdean is correct about newer cars. Improvements in intakes over the last 5 years or so have been made. Dual length intake runners, 4 valves/cylinder (as you have mentioned)and tuned port injection systems are some of those improvements. I am not sure whether 4 valve is cost effective for all makers. Depending on head configurations, cost of another cam, available blocks,..., a maker may opt for 2 larger valves. Older setups are more likely to benefit from the intake mods. So anyway, there is much more to engine and intake design than what we have discussed here, but the fact remains that depending on the application, replacing much of the intake plumbing with a K&N filter kit can improve performance, and possibly, economy. But first before you spend your money, consideration your driving style and the engine. LWF, don't buy a K&N filter or filter kit. You seem happy with what you have.

  • cdeancdean Member Posts: 1,110

    What year is your truck, and what engine do you have, for my info please? Thanks


    i think when you said you disagreed with me on the effieciency thing, you ended up agreeing with me, because you said what i did. Work is occurring faster, so you have to get more horsepower--GIVEN THE SAME MASS FLOW RATE OF FUEL.

    let me explain a little better about the breathing through a straw. assuming you aircleaner is circular like mine, the vacuum caused by the engine creates a negative pressure differential all the way around the the circumference of the cleaner. But air coming in at 37 ft/s in no way is going to go straight thru a paper filter in a 3 inch diameter. air has to flow circularly around the filter due to the pressure differential that is 360° around. now the larger the intake scoop or filter area, the less these effects are. point is air is not coming straight down the tube straight into the engines.

    you were totally correct about the Re #. it was a long day at work, and i made a mistake calculating it before i posted. when i saw the answer, thats why i posted. the 67000 Re# is borderline turbulent, but still makes airflow dependent on geometry of the intake. if yours is straight as a 2x4, it won't be as bad as some honda with a neck that turns 3 times into a scoop. someone mentioned earlier that their truck only had 1 90° turn, i argue that that is considerably more impedent than a straight tube.

    you are not using a large percentage of engine power drawing in air, but it is a percentage, and reducing that could lead to great improvements, especially under high demand situations, like dave said. it also needs to be said that if the exhaust side isn't breathing properly, the improvements on the intake side might not be noticed as much.

    my referring to GMs vortecs is very relevant to the discussion. they improved the engine by allowing it to breathe better. better engineered intakes! that is what we are talking about. they also did tuned port exhaust, with larger pipes, mufflers, and catyls. the intake side was specifically engineered so that air comes through a specially designed shape filter on top of the wheel well, and goes STRAIGHT to intake runners into the pistons. the even did special machining on the inside of the intake runners to make them smoother than the original castings of the parts. they took many, many, many details you wouldn't have thought of, and ended up with 50 extra hp.

    k&n is not going to get 50 hp. but you can improve the performance, especially on older vehicles, because it wasn't until about '96, when chevy found out how much a difference can be made with a well engineered intake. there was a huge tech article in Popular Mechanics about a year and a half ago on the chevy vortec. definitely not for the casual reader, but very interesting and informative on how they improved the engine so much.

    i said before, i don't think the filter alone can do it. that's why i question if its worth it, and if any one out there has put in a filter only and had success, do tell. i might pay 40-50 bucks for 10 hp and 1 or 2 mpg. but i won't pay $300 for the intake replacement.
  • stevekstevek Member Posts: 362
    To cdean:
    I have a 97 K1500 with the Z71 package (whaterver that is). The motor is a 5.7L Vortec with 100K plugs.
  • lwflwf Member Posts: 223

    Great! It sounds like it's all coming together nicely and we agree more than we disagree. One point about the air-filter discussion above, the 37 ft/sec is in the 3 1/2 duct but not through the air filter. In the case of my air filter, its circumference is about 22 inches and its about 5 inches high (estimated by looking at it but not measusred). Anyway, the filter's surface area is about 100 inches as opposed to about 10 inches for the area of the 3 1/2-inch duct; therefore, the air speed through the air filter is only about 4 ft/sec(conservation of momentum). Therefore,I still don't buy that marathon runner's breathing-through-a-straw analogy.

    And as I had said in one of the previous posts, I think a K&N air filter would be the way to go if it's a cheaper alternative for buying filters. But if someone is getting it with the expectation that it will provide a couple of more MPG, I don't think you'll be able to notice the difference. It appears that since the time I made that first declaration of skepticism, a couple of the posts have concurred. Well, I guess we hear what we want to hear.


    Your last post almost seemed like a personal assault on me. Sorry I rubbed you the wrong way because I don't agree with a few of the things you seem to feel very strongly about. But some of us feel that debate is one of the purposes of this "Town Hall".

    You also asked me if I tow. Well, that's why I bought a pickup. It was either that or an SUV. I've had both and much prefer a pickup. I don't know why that's relevant to the discussion that was taking place, but that's my answer. I may have you confused with someone else, but I believe you indicated in one of your posts you are from Saratoga, NY. If so, my towing destination from NJ is up in your neck of the woods, Great Sacandaga Lake where I have an A frame. I recently sold my boat, but I'm sure I'll buy another. But I still have a couple of other trailers which occasionally are hooked up to my pickup with up-to a ton of sand, stone, lumber, firewood, etc. In other words, I didn't buy a pickup because my job depends on having one, I got it because it fits my lifestyle. I've got an idea that I have a lot of company.......but maybe not so much here in NJ.
  • davepercdaveperc Member Posts: 76
    We should rename this thread to Fluid Mechanics, MEs only. Nothing like sitting down and chewing the fat about turb. flow through our intakes for a while.

    The straight filter replacement is not what I would consider a potential benefit. I do argue that improvements can be realized by removing much of the plumbing that makers use. I have a '77 BMW 320i that, among many other mods, has the intake hoses, ducts, and filter box removed and a K&N filter installed directly on the inlet to the flow sensor for the FI system. I don't know what it is like with the stock setup, but am confident that the mod has reduced draft losses and thus improved the overall performance. The next mod I intend to do is to replace the engine driven fan with an electric fan. Being a high rev engine, the fan (no clutch on this one) takes a fair amount of power, mostly when it is not needed (when moving). What do you think? Makes sense, and probably would save more power than the filter mods.

    lwf, You just slipped in before me. I have not read all of 30, but no hard feelings. Sorry if it sounded that way.

    Good questions and thoughts. I figured it was only a matter of time that you mentioned the carb. throut. The head loss is a cumulative function. At a given condition, the head loss for each component can be computed. Many standard situations are given in text books in the form of equivelant length of straight pipe. Using your F150 as an example, I think you said it the duct starts under the fender, into the filter box, into a hose with one 90 degree bend and into the carb. Totalling all the components besides straights there is at least an open end pipe at the beginning, an opening into a tank (filter box), stock filter, exit from a tank, 90 degree bend into the carb throut, all of which have higher equivalent lengths than straight pipe. As a quick example, a standard 90 for 4" pipe is equivelant to 13 feet of stright pipe. Moral of the story is that by eleminating extra losses can help the engine breath. If you were running that marathon, which straw would you rather breathe trough, 5" or 25"?
  • davepercdaveperc Member Posts: 76

    I was asking those questions because you really have me confused as to what kind of improvement you are looking for, if any. You had stated that you are evaluating your F150 cruising at 2000 rpm only. This is not where you would notice a performance improvement. Towing is a more demanding situation. Say you approach a hill, your rig slows, you put the pedal down. Now airflow is not dependant on the throttle plate anymore but on the restriction of your intake.

    Enjoy the lake. Stop by SS and play the horses. Season starts next week.
  • cdeancdean Member Posts: 1,110
    if your intake is only 4 ft /s, then the breathing through a straw analogy is wrong.
    now if it was 30-40 ft/s, then it might be applicable. man this was fun.


    i don't think the k&n filter will help your truck that much because you have the vortec motor which already has well designed intake. i have a throttle body engine, so it make work better for me. that's what i'm trying to find out.
  • richflynnrichflynn Member Posts: 147
    First - daveperc,
    When I was a pre-driving teen in Brooklyn, my bookie always told me that the only way to beat the ponys was with a whip! Here, 40 years later, I still agree with him.

    I am also very skeptical about the K & N filter. At WOT, I can see a possible improvements. In normal, every day city driving situations, I doubt there would be a noticable improvement.

    If the vehicle is used in a heavily loaded (or towing) situation there is a greater possibility for noticable improvement in efficiency.

    So if anyone installs a K & N filter and is able to quantify the before and after differences I would be very interested.

  • lwflwf Member Posts: 223
    I guess I ought to just let this fade away, but something that stanford and cdean both stated has been really bothered me the last couple of days, and that is their conviction that a lot of HP is used simply pulling air through the filter and the ductwork leading into the carb. One said 10 to 15 HP at WOT and the other said a "large percentage". I asked how large, but didn’t get an answer, so I decided to calculate it myself. Fluid mechanics isn’t my game, but I’ll gave it a try anyway.

    Since power is the rate of doing work, that which would be needed to push air at a constant flow past some restricting pressure is nothing more than the CFM times that resisting pressure. After doing the arithmetic to convert all the units appropriately, the equation turns out to be:

    HP needed = 0.00016 * P * CFM
    where P has the units of inches of water.

    I had previously estimated the CFM for my pickup to be about 150, and someone else had volunteered that a good typical value at WOT is 450.

    I don’t know how to evaluate P, but I’m pretty sure it won’t be as high as 5 inches of water based on some fan specs that I looked at today. I suspect it will be actually much lower than 1 for the air inlet system (including filter) of a 1998 F150.

    So if one takes a very pessimistic point of view and uses the largest numbers imagineable in the above equation, i.e., 450 CFM and 5 inches of water, the loss would only be 0.36 HP.

    If one uses 150 CFM and 1 inch of water, the number is 0.024 HP.
  • stanfordstanford Member Posts: 606
    Just a quick note on CFM calculations:

    CFM = CID * Max RPM / 3456

    This formula is good for stock vehicles. Modified engines will flow more air. For an easy test to see if your intake system is restrictive, add a vacuum gauge before your intake manifold. If you see much vacuum, your engine is being air-starved.

    Your 4.6L engine (around 280 cid) would be flowing around 450-500 CFM stock, a very belivable figure.
  • stanfordstanford Member Posts: 606
    About that HP calculation...

    That would indicate the amount of power needed to simply move the air through the pipe. Two problems with that however:

    First, that's measuring the horsepower needed to power some efficient machine to move the air, rather than the cost of trying to move the air through a restrictive element. In fact, that equation didn't even take the quantity of restriction into account (which makes it immediately suspect).

    Second, the figure we need is the cost of air-starving an engine. This is /not/ the same as the cost to power a fan to move the air through.

    As an aside, there are aftermarket fans that you can get to help move the air through your engine at higher pressures (and therefore speeds) then your stock induction system can flow (for whatever reason). They're called superchargers :-) and even they have a remarkably high parasitic cost (though less then the gain they add).
  • lwflwf Member Posts: 223

    Well, I'm glad someone else took the trouble to check the calculation because as I said, this isn't my game. You didn't criticize the formula nor the numbers, so I guess they are all right. Good so far. The idea to try to calculate this came to me yesterday when I noticed that the power-consumption figure for one of those cushion fans used to cool electronic equipment was less than 50 watts for an airflow comparable to this 150-to-450 CFM we had been talking about for engine air intake.

    As far as your comment that my calc doesn't take into account the quantity of restriction, I don't believe that's true. The back pressure I assumed (up to 5 inches of water) is the restriction. And when I looked at what this muffin fan was working against, it made the intake system of my truck look relatively unrestricted. The air from the muffin fan has to go through or over the following. 1) a finger guard that will prevent an OSHA-specified-size finger from getting into the blade, 2) a dust-stop filter, 3) an EMI shield that's a screen mesh with what looked like about 30-percent air blockage, 4) over several circuit boards with all kinds of electronic components surface mounted to it and in the air stream, and 5) out through another EMI-shield panel. As far as I could tell by asking questions, all of that typically represents about 0.2-to-0.4 inches of water. So it seemed to me that when I used 1-to-5 inches of water, I was being grossly conservative in my calculation.

    Now, in regard to the inefficiencies involved in the engine pumping this air, I'm afraid the skeptic in me is coming out again. I think you mentioned a loss of what seemed to me to be very high HP (5 to 40 or something like that). But my calculation indicated much less than 1 HP and I think there's a good chance it's really less than 0.1HP or maybe 0.01HP. I realize there are inefficencies involved but come on now, you can't be serious. I have to believe that if the engine manufacturers could generate an extra 40 HP by spending about 50 watts of fan power, every car in the world would have a battery-driven supercharger for it's carb.

    But that brings up the question of whether or not there is such a thing. I'm glad you mentioned the superchargers. I'm familiar with airplane-engine turbosuperchargers and used to service and change them when I was an mechanic in the Air Force during the days when airplanes had reciprocating engines, possibly before some of you were born. Several years ago, my son bought a Mitsubishi that had a turbosupercharger, and when the turbo housing cracked and had to be replaced, it cost him somewhere between $1000 and $2000. I'm not going to get into a discussion regarding the pros and cons of turbos in car engines, but I do remember at the time wondering why the car manufacturers don't just use a cheap and easy-to-replace battery-driven fan instead of a comparatively expensive and difficult-to-replace one driven by the engine's exhaust. I've never found anyone to answer that question, but now stanford has popped up. You said they are available as after-market devices. Does that mean they are battery-driven fans? And if so, what's the nature of the parasitic costs? The 3-to-4 amps it would take (assuming 36-to-48 watts) shouldn't be a major problem, I wouldn't think. Not if it could provide another 5-to-40 HP.
  • davepercdaveperc Member Posts: 76
    LWF - you slipped in ahead of me again. The program has your text stretched out to be to hard to read like this.

    Great saying. Mind if I use it? I have done my time at the track, but have moved on to bigger and better places to gamble, the stock market. Sometimes the market is no smarter than a horse. Could use a whip on them too.

    Stanford, To clerify: Air starved for this conversation does not mean wrong mixture, it means less air/fuel mixture. Carb's and FI systems are devices that measure the airflow and then mix the proper amount of fuel for efficient combustion. To add to your second point, the problem of air starved engine is not loss of power due to too rich mixture, but the potential gain from increased air/fuel mixture reaching the comb. chamber.

    Power increase and fuel economy are getting mixed up here. These two conditions are very different and should be discussed separately.

    Fuel Economy: When an engine is cruising (non-extreme), the throttle is controlling airflow, in effect starving the engine to maintain power equal to demand. At this condition, increased power(remember, power is being limited) is not the issue, fuel economy is. The only economic benefit I would expect would be the reduced work. But since the throttle regulates airflow to regulate HP, the pressure drop is the same whether the intake is freeflowing or not. The difference would only be throttle position necessary to establish and maintain the needed airflow. This is why I am sceptical about the fuel economy gains. I don't know of a condition where you would reduce the power needed to move the air, except at open throttle, and this condition is too rare to expect a noticable increase in economy.

    HP: Increased power from reduced intake system pressure drop is ONLY possible at high demand, at WOT. Less than WOT, the throttle is regulating power. At the WOT, airflow is limited by the capability of the intake system, not the throttle anymore. This is where the "air-starved" engine condition is applicable. If the intake is restrictive, airflow is less. If the intake is freeflowing, airflow is more. At high demand, if more air flows, the fuel system measures more airflow and thus injects more fuel. Now we have more power because we have increased the amount of air/fuel mixture in the comb. chamber. And at this condition, the RPM is the function that determines what the airflow rate is. At low RPM, the gain is less than at high RPM. This is because airflow, and thus the pressure drop, is low at low RPM.

    This is why I believe the only possible gain that is realistic is INCREASED HORSEPOWER AT HIGH DEMAND, HIGH AIRFLOW CONDITIONS. Again, this is dependant on your vehicles plumbing. The more twists, bends,... the more pressure drop.

  • davepercdaveperc Member Posts: 76

    Just a quick addition based on 38 you just posted. There is a huge difference between moving 450 cfm with no differential pressure to overcome, vice the supercharger stanford is talking about. Superchargers are taking air at atmospheric pressure, and compressing it to about 10 psig. This takes much more work. The power increase is not from better efficiency, but more air/fuel mixture. Supercharged engines are more responsive than naturally inspired engines because the air is forced into the comb. chamber by a larger DP, ~20 psia (14.7 psia + 10 psig boost - comb. ch. presure of an assumed 4.7 psia) vice 10 psia. I think that 4.7 psia is a bad #, might be more like 10 psia, which would make the above 14.7 vice 4.7.
  • AirwolfAirwolf Member Posts: 142
    Ok, since I was an original here, but know nothing about this fluid mechanics converstaion, let me give my $.02 on my new K&N air filter.
    I have a 96 Mustang Cobra, normally about 305 HP (on a good day). Since I put in the filter a week ago, I have noticed on a small improvement in my acceleration. The engine seems to shift better because it can catch up with the RPMs faster.
    So far.... that's it.

  • lwflwf Member Posts: 223

    OK, that makes sense. The little cushion fan I saw certainly couldn't doesn't look like it could put out 10psig, but on the other hand that Mitsubishi impeller, as I remember it, didn't really look all that impressive either. I only looked at the one that was replaced on my son's car for a minute or two, and that was a couple of years ago, but it seemed to me the impeller was only about the size of this cushion fan I mentioned. Are you saying it probably puts out 10psig? The superchargers from my Air-Force days were huge, with two impellers that were about 2, maybe 2 1/2 feet in diameter (the engine was a Pratt Whitney R4360, if that means something to anybody). I could believe that supercharger could put out pressure such as you are talking about, but the one on that Misubishi looked like a toy to me, a pretty darn expensive toy at that.
  • dunbartondunbarton Member Posts: 46
    Hey Guys,

    I think I'll just stick with a $10 Fram filter every 6 months.

    If modified air intake from the factory gave 1-2 mpg, why wouldn't the engineers do it and boost their overall average mpg on all cars to satisfy the nerds in the EPA?
  • akjbmwakjbmw Member Posts: 231
    But a K&N looks way cool in with all the other BMW engine stuff for driving "spiritedly"!
    Sometimes looks count for far more than measurable or tangible results.
  • lwflwf Member Posts: 223
    I agree with dumbarton’s point of view 100 percent, of course.

    BTW, I notice some of you are providing cute little quotations with your posts. The one I’ve always liked and which I think is appropriate for this topic is "IF IT AIN’T BROKE, DON’T FIX IT!"

    But getting back to the 10 psig that Dave implies is typical of supercharges available for cars (do any trucks have them?), when you go through the airflow x pressure calculation, the required power to maintain 450 CFM at that pressure is about 20 HP. And as had been pointed out to me a couple of times, whatever device is generating that 20 HP isn’t going to do it efficiently. So assuming it would be only about 50 percent efficient, that would mean your engine will have to sacrifice about 40 HP just to run the supercharger. Sounds fishy to me. I have a garage full of tools that run off IC engines-----lawn mower, tractor, wood chipper, snow blower, chin saws, weed trimmers, etc. I get an awful lot of work out of those, and all together they don’t add up to 40 HP, so using that much just to spin an impeller wheel to compress the air going into a car-engine’s carb is a little hard to accept. Something is missing here. I don’t know what, and I don’t think I’m going to find out. Not in the immediate future, anyway.

    The aircraft turbosuperchargers that I worked on and installed years ago when I was in the Air Force were a different story, I think. Those piston-driven-engined bombers flew at an altitude of up to 40,000 feet where the temperature was about -70F and the atmospheric pressure was less than 3 psi. That meant the air had to be compressed before it entered the engine; otherwise, there wouldn’t be enough to support combustion. But to supercharge a car’s engine just to compensate for what I consider to be almost imperceptible restrictions in the engine’s air-intake plumbing seems like a gross overkill.
  • lwflwf Member Posts: 223
    Sorry about the misspelling dunbarton. It happens to me too all the time.

    lwf (AKA lqf, lef, lfw, wlf)
  • dunbartondunbarton Member Posts: 46

    Great quote and I use it all the time ..... !!

    I enjoyed your expertise re: superchargers.

    I am digressing from this forum here (a little) but ..........

    May I make another point on the small selection of superchargers on current new cars, namely the Buick Regal GS and Riviera (I know Pontiac "borrowed" this from Buick but essentially it IS a Buick 3.8 V6).

    If anyone out there is contemplating supercharging a FWD V-6 from ANY maker ...... DON'T. Front transaxels won't take it.

    A Buick (GM) engineer told me that GM holds their FWD engines to 250 hp (except Cadillac who does their own thing with the Northstar). The front wheel drives wont take much more and there is of course a safety allowance here.

    Since the Buick supercharged V-6 is rated at 240 hp (vs 205 hp) it doesn't seem like much of a gain from a superchager but that is the reason.

    There was talk for some time that Buick would resurrect the Grand National but it won't happen with a fwd today (maybe later but I doubt it).

    And, a Buick tech who specializes in the Grand Nationals claims that the K & N filters are more hype and rhetoric than anything else (his opinion, not mine as I simply don't know)

    I have posted a "ball breaker" in the "Coupes" section under the guys who like (love) the Z28 Camaros (hey, I do too) vs the SIX cylinder Grand National but didn't get any takers. Check it out...... dunbarton
  • dunbartondunbarton Member Posts: 46
    PS lwf ........

    It's DUNBARTON, not DUMBARTON. I know I ain't too quick sometimes but geez, I'm still your friend ....................? DUN
  • lwflwf Member Posts: 223

    I saw it right after I hit "Post", but it was too late to do anything but send a follow-up apology.

    And that was interesting information you provided which I didn't have. A V6 gets 240 vs 205 when supercharged.
  • dunbartondunbarton Member Posts: 46

    Since you have had some experience with superchargers, and I don't know if you have had any with automobiles, I don't have any info on the Buick superchargers but they can't be too drastic with only a 15% hp gain. When I was more involved with some drag racing in my younger years, a decent supercharger would boost hp by about 50%, more or less.

    Off to see the "Coupes" Z28 section to see if I rattled some cages .......

    By the way, you are forgiven ........ Dun
  • cdeancdean Member Posts: 1,110
    i've got a headache, and don't feel like debating all my shot-at theories, but i will say this. if you want to look at power as a function of the air flow or pressure difference, your "fan" equations don't do it. i apologize for my lack of explanation or maybe i just don't understand where lwf is coming from, but right now, i say those equations don't work for this situation. the way to get power that i would suggest would be to find the force it takes for each piston to move under the vaccuum created by the pressure differential ( the vaccuum at the butterfly intake). the pressure acting over the area of each piston(bore) creates a force which moves thru a distance(stroke) which is work at a certain speed(rpms), and horsepower is 550ftlb/sec. my quick calcs of a chev 350 with a 5 psig vaccuum at 2000 rpms is a loss of about
    2 hp. any comments or corrections.
  • cobra98cobra98 Member Posts: 76
    I thought I had the answer!!! I was watching "My Classic Car" today and they were modifying a GM pickup truck to see how much more horsepower they could get out of it. The first thing they said that they were going to do was replace the air filter. I thought, "oh please oh please oh please, use a K&N so I can be the hero at Edmund's Pickup conference" Well they didn't. But here's what they DID do. They replaced the stock air filter with an ACCEL (the same company that is known for ignition components), followed by underdrive pulleys, synthetic motor oil and a flowmaster exhaust (from the catalytic back). They then dyno'd it and ended up with I believe 19 more horsepower (159 stock to 178 modified). Unfortunately, they didn't dyno it between each change. That would've been real nice to see. But, as they were doing these changes, they mentioned that sometimes synthetic motor oil can provide a 1 - 3 % gain in hp. I guess we could start a new discussion concerning this :-)

    Oh well, I just thought I'd pass this along...
This discussion has been closed.