K & n filter

Just curious are the k & n air filters worth buying or are they just a waste of money?

Just asking as I've never had one, 

I fitted one to my Jimny, air flow should be better, but I didn’t notice any difference in performance. I did however, get it for a good price ( got it at DemonTweaks) and the fact that it is cleanable I thought it was worth the money.

I remember they were the must have filter for cars and bikes in the 80s, but if you are getting one for a performance upgrade, I think you will be disappointed.

I only have mine because it's cleanable, which only makes sense if you are doing the mileage and keeping the car long enough.

Short answer - never again.

Long answer - I fitted a K&N filter, not just the replacement panel, but a complete "pancake" filter assembly to a Suzuki Swift back when I was into "hot hatches" - the OEM filter assembly was in the way of an upper strut brace - not only do the filters "not filter properly" (meaning they allow dust through), they shrink and then do not fit/seal properly (I'm talking about a K&N filter element in a K&N filter housing) and allow even more dust through.

Hi 
I also have one fitted, the long answer below in summary is - Yes and No.

Does it improve performance?  - No, Not in any noticeable way on a Jimny.

Does it improve MPG - No, not noticed any improvement or loss.

Can they be reused? Yes, and like Lambert that's why I fitted one.

Do they filter as well as a paper filter? No, they are in no way as good as a paper filter at "filtering". They working fine at stopping the big stuff, small children, birds etc, but the micron sized stuff they have issues with. That said I've never had any issues running them and I am old and covered many, many miles with them. If I used my Jimny in dusty or sand conditions I would stick with paper, but on UK roads and the odd trip off road no issues.

Do they shrink ? Yes and No - Over time I had one shrink on my Scimitar GTE (pancake filter), but it was on top on the engine getting baked. All those I have that are fitted in a remote filter box away from direct heat, such as my motorcycles (and the Jimny) , these have been fine. That said it took Years for the Scimitar Filter to shrink slightly, it was not an overnight event.

Are they worth it? Yes and No.    If you like the clean and reuse element or just want one then Yes.  If you are expecting any improvements then No.

Just my experience, that of others may differ.