So What's New About K & N's (In)Efficiency Then?

This report (see link) doesn't tell me anything that I did not already know. I've seen countless cars on the rolling road with K & N Filters fitted and the resulting power drop-offs.

Do yourselves a favour guys and steer clear of them unless, as I always say, you are doing the Paris - Dakar or crossing the Nul Arbor Plain in convoy!

Stick to an OEM filter or a non-oil impregnated type from BMC, Jetex, Pipercross or Ram Air.


ISO 5011 Duramax Air Filter Test Report

Interesting - thanks for the link.

Interesting. That appears to pretty much conflict with the tests that I have seen published in some of the books I have.
Since I know nothing about your background, what has lead you to dislike them so much?

Originally Posted by DIY Si

Interesting. That appears to pretty much conflict with the tests that I have seen published in some of the books I have.
Since I know nothing about your background, what has lead you to dislike them so much?

Ditto

Oil is volatile. Heat it up and it will migrate - and just where will it migrate too?

My background? Have you got a couple of days?

I find it extraordinary that people cannot think laterally and not see how paper impregnated with oil will reduce airflow throughput via a given area.

My background - are yes. MIT - fuel management system design (FMSD) - GM - introduction of EGR valves - FoMoCo - FMSD for the odd International rally car here and there - BDA development for rally cars - thousands of hours on dyno and rolling roads - tank design - s/s fuel pump systems for Lancia Stratos, Chevette HSR, etc..

Marine engine development of 427 Holman & Moody engines for racing Rivas, fuel pressure regulator development for Iso Rivolta and Ford GT40 ..............

Common sense in spades.

BTW I don't "dislike" K & N filters, I just liked people to have that extra edge when competing - namely less power drop off from air filtration.

Incidentally all air filtration systems will cause optimum power drop off. Some filters more than others.

Fair enough! It's just some of the time when I see K&N/any brand of filter bashing type threads, they are often from folk who know very little about the business. You, Sir, appear to very much the opposite. In my case, I've needed filters capable of holding lots of crap and be fully exposed and still working, and have seen test showing no appreciable flow drop even through 1/4" or dust on a K&N. I am, however, willing to be shown different.

If you are doing/have done what you said then I am really surprised that you don't know that ALL BMC filters, whether CDA, DIA, cones, panels, cylindrical, twin cones and their motorsport applications are oiled.

I know that they are, it's just that K&N where the only people who ever had any filters in stock for my carb. Not easy finding a single filter for a 48 IDA webber. And as I said, most of the tests I've seen say pretty much the opposite of the one the link shows.

Originally Posted by DIY Si

I know that they are, it's just that K&N where the only people who ever had any filters in stock for my carb. Not easy finding a single filter for a 48 IDA webber. And as I said, most of the tests I've seen say pretty much the opposite of the one the link shows.

I don't like K&N personally. But this has nothing got to do with the filter medium. Even the qouted test shows that the flow rate of a clean K&N is better than any of the other tested ones. And up to a certain point the flow rate is better than any other of the filters too.

The point with the oil damaging the AFM has never been validated. AFMs on standard cars go as often as on others. I am working in the industries for nearly 3 decades now, starting when the AFMs we use today not existed and have seen since the introduction those going on a regular basis.

Many cars that come to me and my associates for performance tuning we have to send away because of faulty sensors, where often the AFM is the problem (i am not getting involved in the repair/rectification of such problems).

It also must be clear that a exceptionally well flow characteristics has got some draw backs. But the question here is, whether it will outweigh the benefits.

K&N sells over 2.5 million filters annually, which is about 50,000 a week. If the damages were to the AFMs and/or the filtration rate damaging a company like K&N would not exist anymore.

Also the statement that K&N filters lost power is not a scientific statement. Again I want to point out that I do not like K&N (because they could do better in many ways) but blaming K&N this way is not correct.

A lot of the so called induction kits are as a matter of fact only a filter on top of the throttle body. This will loose some power due to what they call heat soak. But this is only applicable when the vehicle is moving slow. What makes the difference is that the short induction will kill torque.

Ultimately you can get a lot of power with such a short 'induction' as this is required when high rpm is that is required. Hence a lot of the race induction kits that are available from Japanese car manufacturers race divisions are short and in rather hot places.

But to make a proper induction you need more than a filter. Induction design is very similar to exhaust design in its principles.

This means just having a flash name or a carbon pipe and a filter is not making anything a proper induction kit. There is a bit more involved.

BTW, your application is a very tricky one to solve.


Edit: My previous poet was not directed at you. Sorry, if you misunderstood me. My bad.

Originally Posted by CPH

If you are doing/have done what you said then I am really surprised that you don't know that ALL BMC filters, whether CDA, DIA, cones, panels, cylindrical, twin cones and their motorsport applications are oiled.

Not quite a slip of the tongue! I am aware of the fact that BMC filters are oil impregnated but should have been more definitive. I shall not go into the positive or negative merits of BMC v K & N but there are some differences as I'm sure you know.

When we were using the magnesium Dell'Ortos on Rotax 250 engines, as clean air as possible was essential for obvious (two stroke) reasons and certain filters were discounted. Certain oil impreganated filters were, in fact, recommended.

My experience with carburation, MFI and latterly EFI started before most of you were born ( ) and ended about 10 years ago. I did, before leaving for France, still help out on setting up carburettors on the rolling road. K & N has always, as far as I can see, been more active in the UK market, therefore I have seen more of them. In virtually every case there has been a power drop off that has been reduced by fitting a different kind of filter. This has also been true of cars with EFI.

I do not condemn all oil impregnated filters out of hand as they do have their uses, particularly if you are competing in extremely dusty off-road events. Even then they tend to be used as part of a primary stage filtration unit. The important thing in this type of application is the cfm airflow through a given area - this can be anything up to 6 times the area that would, under normal conditions, provide the engine's requirements - and the time it takes for the primary filter to reach the stage when the engine's air flow requirements cannot be met. This can mean filter changes after only a few hours in very severe cases.

Paris - Dakar type events provide a great deal of real world data for air filter producers. Not much has really changed during the last 10 - 15 years but a lot of lessons have been learned. An early one was the requirement for a secondary air filtration system to reduce the chances of oil contamination of MAF sensors and suchlike.

I have (or had) no commercial interest in the recommendation - or otherwise - of any particular make of air filter or air filtration system. My primary objective has been purely to find the units or systems that caused the least power drop-offs over a given period. By this I mean it's no good fitting a filter that is a 9 day wonder - and there are a few of those about!

Under bonnet temperatures became an obsession with me from the time that I was the East Coast technical representative of a well-known manufacturer of British GT cars. In Florida it was noticeable that a number of engines fitted with SU carburettors were suffering cylinder head/valve damage whilst those fitted with Webers were not.

A forensic engineering exercise resulted in my finding that after some time, particularly during very hot weather, the needles in the SUs were lacquering up due to the formulation of US super octane fuels. This altered the needle taper thus causing the engines to run leaner with the results that you would expect. The Webers, being differently configured, did not.

The result was that it became a servicing requirement for the needles to be "delacquered"! Incidentally I also suggested that the needle valves and seats in both makes of carburettor be cleaned too.

Over recent years under bonnet temperatures have increased considerably, in the main due to global warning. This has caused manufacturers a great deal of trouble with fuel vaporisation and air filtration systems.

Happily Alfa-Romeo has always had exceptionally efficient air filter systems but then its cars have always had to survive southern Italy and Sicily with hard driving!

Whilst on the subject of the increase in under bonnet temperatures, another side effect has been the shortening of the life of both auxiliary and cam belts which also suffer from extremes of temperature change. I suspect that this is the reason why failures have started to happen at lower time/mileage spans and manufacturers have shortened the time/mileage change period.

Air filters are now also seeing a shorter life for the same reason as road debris, tyre dust and carbon emissions are all on the increase due to the rise in temperature. Even the change in brake pad material has contributed to this very considerably!

For this reason, it is my opinion that the best type of air filter is a non-oil impregnated one though some oil impregnated ones are better than others depending on the quality of the material used and the viscosity of the oil.

Induction systems are also going to be subjected to increased under bonnet temperatures and their benefits could be reduced for obvious reasons.

I'm sorry I've rambled on but this whole area (fuel management systems) is one of my hobby horses.

Perhaps I can persuade the odd air filter manufacturer or two to part with product for real world testing and this could form part of a section for testing all kinds of products; perhaps more of that in the future ?

I can accept that statement.

This leaves us with the oldest problem in the history of transport/racing: Horses for courses.

Flow rates affect performance. Question now is what has got priority?

But one more point, which I have given in my career a lot of attention is trying to avoid problems as far as possible.

One way to do it is not having a cold air feed. If it is inevitable, then I try to direct it in a way that the least amount of particles can hit the filter directly. In all other cases I look for places that are cool, fairly still but able to get enough supply and can't starve the intake from air at high speed.

Originally Posted by CPH

I can accept that statement.

This leaves us with the oldest problem in the history of transport/racing: Horses for courses.

Flow rates affect performance. Question now is what has got priority?

But one more point, which I have given in my career a lot of attention is trying to avoid problems as far as possible.

One way to do it is not having a cold air feed. If it is inevitable, then I try to direct it in a way that the least amount of particles can hit the filter directly. In all other cases I look for places that are cool, fairly still but able to get enough supply and can't starve the intake from air at high speed.

I reckon the stiller the air the better. This leaves the wheel arch and preferably the one opposite the site of the original filter housing. Sadly this would not work with the Q4 but the car still manages to hit the rev limiter in 6th on a hot day (on the autobahn)! What I do have to do is check and/or service the airfilter evry three months or so.

At this juncture I would like to point out that I'm rarely in Germany and I do not let the car hit the rev limiter very often !

Originally Posted by AntMat

My experience with carburation, MFI and latterly EFI started before most of you were born ( )

So iam only 29... no dissrespect, but whats that got to do with it? My 15 years experience tho not as long as you still accounts for something (to me anyway )

Originally Posted by AntMat

Perhaps I can persuade the odd air filter manufacturer or two to part with product for real world testing and this could form part of a section for testing all kinds of products; perhaps more of that in the future ?

Do it! would be good to see the results

Originally Posted by CPH

I can accept that statement.

so do i (apart from above!) under bonnet heat is a big issue for alot of reasons most people don't understand, that is the other reason i stand by the "still airbox" over cone filter debate

Oh, for the record, iam well aware of intake tuning (similar to exhaust tuning) the difference unequal intake tracks make to torque curves and the such, making plenum chambers more favourable for normal road applications than ITB's

True, but equally for road applications, a little bit of extra induction roar isn't always a bad thing.....
Still air around a filter/intake is always a good thing. Anything that helps smooth the air entering a system is generally worth a little bit of bother. Even better if you can locate it in a high(er) pressure area too. I managed it on my mini, although it did require a rather unsightly bonnet adornment. But it did crate a nice high pressure area around the filter. So much so in fact, that in the wet you could see it affecting the air flow! It generated enough effect to drag the washer fluid down the windscreen at anything over 50 MPH. Which I don't think is too bad given the slab fronted nature of a mini.