Maybe some K&N filters stop more dirt if properly lubed but, mine don't. Take a good look at the screen in your screen door. That is about what the K&N is like.
In order for the oil to catch the dirt/dust, the fibers must be soaked with oil. If their are no fibers over some of the holes, how is the oil going to catch the dirt coming through them holes?
Besides, you are supposed to lube the UNI as well. If the UNI is properly oiled, can you see threw it? Maybe its not the filter, maybe its the oil. I know, I'll use the K&N oil on my UNI. Then I'll have the perfect filter.
Like I said before, I have a K&N filter, but I run a UNI. If I want maximum air flow, I'd put the K&N back in. If I want to protect my engine from dirt/dust and still have better air flow than stock, I leave the UNI in.
I don't mean to start a pi$$ing match, but you'll never convince me that the K&N is the best overall. Their is a pretty basic reason it flows more air, think about it.

 

I second that. Several trips to the sand dunes with both have done it for me.

 

K&N will flow more, but that includes micro particles of dirt and sand. They also are very sensitive to oil amount. I'd worry more about dirt then sand, as sand is relativly coarse compared to dust. I'd also worry more about a 2 stroke then a 4 stroke as the 4 stroke is only wearing rings while a 2 stroke is having its lower end worn away. So I'd do it like this:


dirt all, uni
sand 2 stroke, uni
sand 4 stroke k&N

IF you maintained it EXTREMELY carefully, you could run a K&N acceptable. I keep 4 for my banshee and change after a full day of riding. Now, if you're that carefull....Of course, I also just throw on a uni filter as an outer wraps when I don't want to worry about it...

 

"Properly oiled the K&N has been proven to catch more, and finer dirt particles than any other filter"

Where did you get that information?

 

with the k&n it is better to add a pre-filter on it to keep dust and crap out,i've ran severals k&n oiled filter with k&n oil air filter and you'll have a great surprise when you take the carb apart or a look into it,the oil make build-up easily and gummed the carburator intake valve as well...

 

I do not know about it being a proven fact. I belive that a K&N flows the best but I to don't think it protects the best.
Here is some information from AMSOIL. FOAM filters Go to the chart at the bottom
Air Filters

 

I have a K&N uni filter with a pre filter. Is the K&N uni filter not the same as a uni filter?

 

No there is no such think as a K&N uni
K&N is a K&N, A cotton gauze style material squished between metal screens.
And UNI filters are foam

I have used both off road and on the street, and in my opinion K&N is a better filter for performance and filtration. I have never found dust or mud in my intakes since I made the change like 10 years ago and that includes so pretty dry K&Ns. but I have seen dirt build up and destroyed engines from a lack of oil on a foam filter.
Both filters will allow the same amount and same size of dirt particles threw if not properly oiled. No matter what kind of filter (other then paper) it must be properly cleaned and oiled to work.
As far as performance on my street bike witch spends a fair amount of time at the track re-quires a jetting change if I switch from a high flow UNI to the K&N. The K&N flows allot more and will allow for more power.
A pre filter is a good idea no matter what machine if you are in sand or extremely dusty conditions.

There will always be this argument about what filter is better. Just pick one and look after it properly.