i have a k&n panel filter for my 1.0L k11 micra. the car feels faster due to more responsiveness and is louder, especially when the engine is cold, however it isn't that loud at all compared to a friends xscara and a friends 306, both 1.4s with cone filters, still but worth 35quid ish (thats what mine cost). im not sure if its not so loud due to the small engine or just becuase i am still using the standard box, however my insurance is stil vaild, unlike a bad-ass cone (even tho they are very kool).
a back box alone wud just make a noise, but the filter makes the engine much more responsive, and so it feels faster, as well as making it sound beefier:grinning: