I posted this in another thread, but I feel it should have a thread all it's own. I've added a few things here over the original post. This is for those who use K&N air filters or are thinking of using them. I rebuild many motors for racers and trail riders alike and have seen quite a few come through with air filter related issues. From experience, I can say even the best maintained K&N passes enough dirt to cause substantial engine damage
. Somebody on here said if they're good enough for the top racers, why shouldn't they be good for the everyday rider? Well, the top quad racers using K&N's (the slight few) are probably getting paid to race and are getting paid to use products or are getting them for free, so they really don't care how much a rebuild will cost if they have an engine failure. You really need to consider whether the VERY slight, if any, power gain is worth the cost of replacing a top end. Why put yourself through some unnecessary grief and expense when you can run a foam filter and be safe. I doubt you would be able to notice any performance advantage anyway. And while some will suggest an outerwear, if you're going to restrict the "oh so great" K&N with one of these, isn't that defeating the purpose of the freeflowing filter?
The pics below are of a throttle body from a 700 Raptor that a friend of mine owns. Against my recommendations, he chose to use a K&N. He cleaned and oiled it as to their specs, and he is very meticulous when it comes to maintenence, so improper care was not an issue. This is what I found when he started complaining of hard starting when cold and poor performance. So here is my point, if you follow K&N's recommendations to the "T" like my friend did, and you still have this kind of dirt passing through, what steps do you have to do to insure it won't happen? A lot of times, it can take only one ride to destroy a top end due to excessive dirt entering your engine. Are you sure that K&N you're using is properly cleaned and oiled? Sounds like a risky proposition to me.
By the way, the Raptor top end job consisted of a complete valve job, a re-Nikasiled cylinder (because the passing dirt wore off the coating), piston, rings, and gaskets, all a direct result of dirt entering the engine. If I remember correctly, it cost close to $1000.......he runs a foam filter now!
The choice is yours, I have nothing to gain or lose here, just trying to save you in the long run by giving you my advice from years of experience. Good luck.