Does K n N air filter really work?

K&N are marketing experts - their slickly worded ads are a lawyer's delight! Deciphering the marketing speak vetted by their lawyers:
- Yes, K&N filters have lower restriction than most paper filters. IF, and only IF, the air filter(s) in your intake are the bottleneck/flow restriction, then a less restrictive filter can allow more air flow and thus more power. On most modern cars, the air filter is not actually a flow restriction, and you can remove the air filter entirely and make no more power than the stock paper filter. A K&N can not make more power than no filter at all... So in reality, most cars will not show any increase in hp with replacement of a stock paper filter with a K&N drop in replacement filter.
- NO, K&N filters do not filter better than paper filters - they let through more dust and fine particulates. If you read carefully, they never actually claim to filter better, in any of their materials. Independent tests have proven many times over that K&N filters don't actually filter all that well. They made their reputation in desert racing where regular paper filters could get clogged with dirt, while K&N filters could keep flowing better when dirty. (Part of that was letting more dirt through...)

So, bottom line is they don't actually give more power, and they don't filter particulates as well, compared to a stock filter. Why would you want to use one again? Oh yeah, the marketing guys also say you can clean it and spray oil on it and re-use it - which is true, but often the K&N oil coats and clogs sensors downstream of the filter, causing check engine lights and rough running. Paper filters aren't all that expensive, actually filter out dust and particulates, don't damage sensors, and make as much power as a K&N filter in most stock intake systems... back to why would you want to use a K&N air filter?

Cheers,
Gordon

 

+1
This is the biggest negative when using K&N filters. The MAF usually takes the biggest hit.

 

An old K&N filter will always be worse than a brand new paper filter. For the price of one K&N I can buy 5 paper filters. Given the price difference, my money is better invested in frequent changes.

When I was younger these were the hot upgrade, but the cleaning procedure was (and still is) a bit of a mess and more often than not I ended up spreading dirt on the side that was supposed to remain spotless.To crown it all, the dedicated cleaning solution and the oil were quite expensive for what they were, so I doubt that I ever made any economy with these filters.

Maybe some use for a vintage car with hard to find filters? But these cars are now so expensive that I doubt saving a few bucks on filters makes perfect sense.

 

Same for BMC filters. The also do not provide as much sound deadening as a paper filter, so you will hear induction noise much more. Whether that is good or bad....

 

And I forgot to mention that the filter "installation kits" (a.k.a "high induction kit" in the brochures) should be avoided like the plague. Manufacturers do carefully design air ducts in order to bring fresh air in the engine bay, and most conversion kits are just tossing it all in favour of a filter that is left alone in the middle of the engine bay.

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I had such (ridiculous) setup in my old Renault 5 alpine cup. An old chap just told me "maybe not such a good idea to suck air next to the glowing hot turbo". As he was (much) faster than me I though he was right...

So these cotton filters are somehow "acceptable" as long as they replace a stock filter and do not mess with the air intakes. By acceptable I mean you will save $15 on the next filter change (which is marginal considering there is already worth $300 of oil and spark plugs in my car).

 

While I am a critic (Post #3 above) I am somewhat a tinsy hypocrite.
The one advantage of K&N is it's adaptability. It was the only one I could get to fit on my Koenig 928. However, this car does not have any MAF or electronics down stream to get contaminated with the oil. This is an ALPHA-N(MAFless) System.


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Do not use a K & N filter on anything.
I had one on my Turbo Subaru powered offroad buggy and a lot of dirt got ingested into the intake tubes. I always kept it clean and oiled.
It’s just not worth the gamble that dust will get past the filter. Use an OEM paper filter.


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K&N is really just a variation on the old oil-bath air cleaners that cars had before paper filters were perfected. A real mess to clean. A waste of money solving a problem that doesn't exist.

 

I had a car that I “upgraded” the air filter to a K&N. When it came time to service the new and improved air filter I noticed a coating of dust on the inside on the intake system down stream of the new and more better K&N. It promptly went in the trash.

 

I’m not taking sides on whether it’s good to use a K&N or BMC vs the OEM paper filters but over on the 360/430 forum a member did an actual before and after dyno test. And in this one instance, the claimed increase in HP, was actually measurable. There was an 8 HP gain using a K&N filter. That’s actually the first time I’ve ever seen an independent run comparing the two. Not that you’d feel 8 HP...


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I currently own 2 different brands of exotics. Both brand service advisors told me not to use K&N filters.

 

I used to run International Sales for K&N, in addition to running my own tuning shop for exotics and euros. Including pro-level and club-level race cars and our own team. We had engineers and dynos and tested everything. So I actually have some technical expertise and experience on this topic.

Happy to answer any direct questions about K&N (or any other pleated gauze filter). There is some good info in this thread and some complete BS/False info.

Net/Net - paper and pleated gauze both have pros and cons. OEM's have and still do use both depending on the application. K&N is OE in many all out performance variants as was BMC in Europe.

Paper will never flow as much air as pleated gauze.

As to dirt and dust, yes, that is a potential problem IF you are in an area that it is very dirty. I have used pleated gauze on EVERY race car we had built and that I owned. I use it currently on my very built e46 CSL-style M3 Cab (BMW pleated gauze filter was OE on the CSL intake). We use K&N on the 550. We also saw tangible increase in HP on the dyno with stock v pleated gauze filters.

If you live in the desert and drive a dirt road home, maybe not the best solution. But there is a "sock" that can go over cone filters to pre-filter.

If you drive your car sparingly and want to maximize performance, then it is a great alternative.

K&N actually has a significantly impressive R&D and Testing department with about every piece of test equipment known to man. You would be amazed how quickly a paper filter gets dirty and stops flowing air properly. A pleated gauze filter WILL flow the needed air to your car longer and more consistently.

As for oil getting in the MAF. That is an old wives tale. Yes, it happened to me once. On a filter that was OVERLY oiled and 30 years ago. That just isnt an issue today and hasnt been for over a decade.

YES, people have hurt motors with older pleated guaze filters. The tech has come a long way in the last decade and you simply cannot say that things that happened with that style of filter 10/20/30 years ago apply today (as long you as you use a quality part like K&N, Green, AFE, BMC, etc).

There are crap knock-offs from China and some out of the SW USA. But the reputable brands DO know what they are doing.

 

Brad- I remain unconvinced.

 

Is that a question?

My role is not to convince you. I don't sell K&N or any filter, haven't for years. I am happy to answer questions though.

 

Brad- Not a question.

 

True. And irrelevant, for a stock intake system where the air filter is not a bottleneck or restriction - if a paper filter flows as much air as the engine can use, then it doesn't matter that a drop-in gauze filter replacement could flow more air, because the engine can't take advantage of a lower pressure drop or higher potential flow rate across the filter.

 

This is spot on. However, in nearly every car I ever put on the dyno, we saw gains by increasing air flow. We would start by testing the car stock. Then we would remove the airbox (usually just the cover) and filter. For cars with RAM air, we would simulate 60-80mph airflow. We would then compare how much performance the filter is costing. Then we would test with multiple brands of pleated gauze. We found that very few cars have optimized intakes where the paper filter flows enough air. It is becoming a bit more common in the last iteration of car development where manufacturers are pushing the power war game, but its still fairly rare.

This is especially true with cars with forced induction. You will nearly always see a gain in performance with a *good* aftermarket filter.

But there is a lot going on in a cars airbox these days. We would also measure resonance and disturbance. For example, it can make a real difference if the folds (in either style filter) are going left to right or front to rear in some cars.

The point is that saying "there are no gains and cars are optimized" is a bit naïve if you have not actually done any real analysis and testing. You are just repeating with others have said, who also generally repeating what they heard 3rd hand.

I think these are the 2 most important questions:

Is an aftermarket filter (1) safe and (2) a boost in performance?

1. Yes/No/Maybe - this depends on the filter, the environment, the driving style, the maintenance on the vehicle
2. Nearly always

There are no hard and fast rules. Except maybe one - if you put in a cone filter intake system and don't properly heat shield it (as shown in an image above), you will lose performance as all you are doing is sucking in more HOT air, which is almost always worse than having less COLD air.

I can tell you in the 550/575 and 355/360/430 cars (and everything older basically), the filter replacement 100% gains performance. I have not personally tested any newer models than those so I cannot comment factually other than just to speculate, which is not super helpful.

 

That's also true, but as formatted, it's a big "IF". I know in the Miata world, dyno tests have shown over and over across the 4 generations and 30 years that paper filter, K&N filter, NO filter, all make exactly the same power with the stock intake system. I could point you to those dyno tests, and easily find dozens of other back to back dyno tests showing no increase from a drop in K&N filter. Perhaps you meant the generic "You" in "You are just repeating...", but that's not the case for me. I've done a lot of reading and research on the subject - as an engineer, I can discern and filter the 3rd hand stories from actual data.

Oh, as for the K&N oil fouling MAF sensors - hasn't happened to me because I won't run a K&N filter again after the first and only one I tried in the early 90s, but it's certainly not rare, it gets reported all over the enthusiast forums.

 

Yes, this is often more true on low HP cars. That is not what we are talking about here. But if you just want to argue rather than be open to learning something, that is ok. I will just bow out.

 

Several years ago a forum member had his stock 488 dyno-tuned and gained 70 whp. Then he added BMC air filters and gained another 10 whp.

 

My issue with K&N isn't whether or not they 'work'. They might. They might not. I'm open to learning.

My issue with K&N filters is that they are marketed as 're-usable' after cleaning and re-oiling. In the great tradition of Y-chromosome behavior, "if a little re-oiling is good, then more must be better" and ka-blammo the MAF's are fouled.

 

Yes, this is potentially true. If people don't use the product correctly, then there is a chance of an issue. Hard to blame a product for the issue when it is user error though, don't you think? That is like saying "Judge, I was only going 100mph because I have 700HP, it was the cars fault!"

BTW, the re-oiling is not a K&N thing. It is a universal issue with pleated gauze filters.

Also, the need to re-oil is not common. I typically do it every 3-5 years depending on mileage and environment. I have BMC in the Ferrari, K&N intake on the M3, AFE on the race car and a stock one in the Q7 (as I cannot find a high quality pleated gauze to fit).

BTW, I really don't like K&N as a company (having worked there), but that is not to say that they don't make a good product. I actually had some very negative views toward K&N product prior to working there as well. Most I later found out were internet "fact" that a competitive company put out. In truth, the tech and research that goes into the product is quite amazing and the product evolves yearly.

 

Yep. I knew about the tune gains, but not the filter. Makes sense though, again, high HP cars with forced induction. Both almost always see gains! Thanks for the data and facts. As this is a Ferrari board, that data along with my dyno results on the earlier cars seem to be more relevant than what happens on a Miata.