I´m just regurgitating some of the things, I´ve heard on other boards. And some of my own oppinion. The K&N doesn´t do a much better job (maybe worse) than the stock filter at filtering small paritcules. Very fine paritcules like silicates slip through. A pre filter is recommended in very fine dust or sand. I buy filter matrial at an outlet 3-5 micron and make my own prefilters. A square yard of tacky 3-5 micron filter material half an inch thick, will make three or four pre filters (accordian style) and can be washed and reused. The pre filter can be removed quickly, on the road, if it becomes plugged. The prefilter doesn´t seem to help nearly as much with the OEM paper filter, very fine dust and moisture turn to cement in the filter. Where in the oil soaked filter (K&N) the fine particules don´t bond (can be washed back out). K&N seem to take a light bath much better than the OEM type filters. Though submersion will turn both into a wad of junk, the K&N can often be straightened and used again.
It´s beens said the K&N doesn´t flow much better than the stock filter. Well maybe both being new that´s a fact (or close) but I can tell you from experience, the paper filter plugs up (becomes restricted) pretty easy and is almost impossible to successfully clean.
I know the K&N holds up better when wet, I thrown away many paper filters, due to moisture.
Throttle responce, seems to be better with the K&N for a longer period of time. A new OEM filter starts falling off on flow pretty quick. Don´t know about HP claims. An OEM type filter and a K&N replacement for the OEM filter are probably pretty much the same in overall HP. The biggest restriction is probably in the plumbing not the filter. K&N´s always seemed to me, to improve throttle responce some.
