RzR 4 Air Filter

Just had my 2011 RZR 4 800 just had to have the engine rebuilt, Used a K&N filter earlier then switch to Uni Filter, the engine rebuild was do to pitted valves and pistons.
tested the rzr in Glamis and came back inspected filter and dust was still getting by filter.
does any one have a better filter system they can recommend ???
thanks
SMT450