K&N Airfilter - Have one long term, any issues?

I fitted a K&N a couple of years ago, mostly in the hope it would give a bit more performance, it probably didn’t make any difference, but then I got it at Demon Tweaks at a very good price so can’t really grumble.

My other car has just been treated to a new bog standard air filter, cost about £12, the one that was in there had 2014 written on it and none at the garage thought there was any problem with it. Still I can’t really feel any difference with a new filter. It’s ironic really a lot of things are changed before they really need changing at most services.

First - K&N "filters" aren't really filters, at least not in the true sense of the word - it's a wire mesh frame, supporting cotton gauze coated with a proprietary "tacky" oil. The concept is that as the air flows through the spaces in between the gauze, the dirt particles get stuck to the oil and stay there.

They "flow better" because there is less restriction, and there is less restriction because there is more space between the fibers of the "filter medium" - there's more space for air to pass, there's more space for dirt to pass, and hopefully it gets stuck to the oil.

Incidentally, if you read your K&N cleaning instructions you'll find that they advise against regular cleaning, claiming that a dirty filter filters better, it's more clogged so there's less space for dirt to pass without coming into contact with already trapped dirt.

Long term effects - every K&N filter I've owned has shrunk, the rubber surrounds that support the mesh that supports the gauze has shrunk so that it no longer fits the filter box and no longer seals properly, so dirt can pass.

I will no longer fit K&N filters to anything I own.

I can't say I have ever noticed the surrounding seal shrink on any of the vehicles I have had k&n filters in which has been virtually every car I have had for the last 20 odd years. Their build quality has always been very good in my experience.

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Can't say myself that I have experienced them clogging up quicker than a paper filter, and cleaning, if done properly, uses very little product in my experience.


 

I don't have any references these days, but I'm sure Google would turn stuff up. But there have been plenty of flow bench tests over the years. These tests have shown that after some use the K&N tends flow less than paper ones with the same use.

All said and done, I think the differences are likely to be small. Neither is going to transform the vehicle. But if you add up how many paper filters you can buy for the cost of the K&N filter + cleaning kit + re-oiling kit. Then the K&N just seems very expensive most times.

On a full out performance or race car I can see they might be worth it. But a regular low powered non-tuned road car/4x4 I struggle to see the ROI.

Just looking at the relative costs, I paid 37 for my filter and a clean kit is 19 from halfords. ECP sell a Mann filter for 15. So rounding up one K&N gets you 4 good quality paper filters or 36k miles. I guess if you are not daily usage of your Jimny and or you don't keep your cars more than 3 or 4 years then it might not be worth the K&N but if you do daily it then the cost is favourable.

First - I agree with your comments of the ROI when used on a road car.

I fitted a pancake style K&N to a modified sport hatch, primarily because the OEM air filter housing occupied the space I needed for a suspension brace, I did not expect an increase in performance but there was one, and there was a slight but noticeable drop in fuel consumption. I went through two different K&N filters on this vehicle and found them to be poor at filtration, and both elements shrunk causing sealing issues.