In a recent Roundel Tech Talk (May 2011), Mike Miller stated "7) I think drop-in oiled cotton gauze air filters are a waste of money, and function mainly to allow larger dirt particles into the engine,". I'd like to get the opinion of other club members on the issue of paper filters vs K&N type filters. I've investigated this issue a bit and found some very interesting information at the K&N website http://www.knfilters.com/air_filter_testing.htm.
What data/research/testing has he done to support his claim? I'd like to see his Oiled Cotton-Gauze FAQ Sheet that he references in his answer. I need to see his proof or I'll have to believe the plethora of supporting data in favor of this type of media.
You can go to Roundel Tech Talk and ask Mike Miller for a copy or you can send me your e-mail address and I'll forward a copy to you. This document dates to 2002 and s does not include any test data.
It's been quite a while since I've read the study, but one was done using good experimental practices (in my opinion as a former chemical research lab technician) in the early 2000s. Air with measured sizes of particulate matter was introduced to the filters and measurements were taken of the amount and size of particles allowed to pass by the respective filters. The K&N type was clearly inferior in admitting more and larger particles. If you read their page carefully, you'll find that this is the information they omitted. While their filters are "between 96% and 99%" efficient at stopping the 'standard' dust mixture, the usual paper filter is probably above 99% efficient because the independent test says it's better at this. K&N claims higher flow capability through the filter, which is true. Their power claims are all "up to", never "at least". NOWHERE will you find K&N guaranteeing even a one horsepower gain on any BMW. Every term they use with regard to increased torque or horsepower is hedged or qualified. When you read everything carefully, you'll realize that what they don't say is at least as important as what they do say. What they do not say is that any BMW will have a higher flow rate through the cylinders. That's because it won't. At least not due to changing air filters. BMWs have overcapacity through the filter. The flow rate restrictions are in the head - the valves and cam profiles - not in the air intake system. This is why you'll see no real measurable gains from a K&N type filter. While your engine may not be harmed during a normal lifespan from the additional particulates allowed past a K&N type filter, neither will it benefit. In light of the potential harm and no benefit, I won't use one. After all, I run engines well into their third hundred thousand miles (over 250k on The Kelvinator right now). Even slow degradation will show up. The choice is yours, but don't delude yourself that you're getting anything other than higher intake noise out of a K&N type filter.
Dear CR, I suggest you go to the K&N website and learn how K&N tests its filter in accordance with recent ISO standards. http://www.knfilters.com/air_filter_testing.htm I'm certain testing improvement have been made since the early 2000's. However, everyone must judge for themselves, scientific fact vs here-say.
CR has it right here. People are easily influenced by slick marketing, especially when they do not have a technical background, on stuff like this product. Take the E39 M5 for example...K&Ns are known for many years for fouling the MAFs on the M5. However, the only "mod" they do for the M5 is to create more cylinder wear due to less effective filtering than the factory filters. The M5 has a massively oversized dual air intake system, and even Dinan has shown that their custom $2k CAI coupled with an ECU tune only gives about 4hp on the 400hp motor at the peak with obviously less gain everywhere else. However, nothing one can say, no matter how sound the technical details, will convince those who have already made their decision based on the marketing. Sometimes its good to have a significant background in fluid dynamics, particularly internal fluid flow.
Here is another data point based on ISO testing by some independent owners on OEM vs. K&N filters (read oil impregnated filters). Not the end all, be all, but just another data point. http://www.shipkiller.com/AirFilters.html
I'm not dumb. I read the K&N site first. Apparently not. The standard is ISO 5011:2000. That means it was codified (but appears to stem from an earlier SAE test) in 2000. What do you think has changed? Dirt? Airflow? This is all simple physics and methodology. All it needed was a uniform standard. These tests could have been run in the '30s. Outdated or not, this is the standard K&N was testing to. It's right there on their website. Delightfully enough, someone else went to the bother to dig out the article to which I was referring. I had actually forgotten that the K&N clogged faster. Since you're supposed to clean them regularly, I'll overlook that. I'm more concerned with what gets through them (more and larger particulates) than what doesn't (air). Those are the scientific facts that K&N doesn't want you to know. So they just talk around them. Otherwise, they'd be out of business.
you've posted 2 links that are both to the K&N website, obviously they aren't going to say anything that would make the filter seem like a bad idea. this wasn't the article Krieger was referring to but I'd suggest reading it http://www.bobistheoilguy.com/airfilter/airtest1.htm
Snake oil, stay away from K&N or ANY of the gauze filters. They do NOT filter as well as OEM paper filters. There is NO performance gains, just more noise. Mick
