If yours is stock than stock filter is fine or go to the k&n filter There's lots of write ups you can research by using the search function .. like raising the wye on top of the stock filter box to a whole stage 7 or the Morley's equivalent plus upgraded exhaust.. watch out for the mod monkey he hides in all the past threads ..
I may have a used stock K&N filter, I have new of course, and I have the DJ stage seven or our Morleys Muscle jet kit if you have a full system and want to maximize the engines potential.