i did mine around like 14,000 miles ago...havent had a problem with it, the K&N i have to clean and oil it every so often, and with the air intake suckin in mud and water and stuff...i dont really do much off-roading though. i will tel you this though the stock xterra s/c really has no nuts whatsoever when you compare it to other vehicles in it's class, but after i put that pulley and the air intake on you could feel a huge difference, i actually raced a stck s/c one and i beat him by about 3-4 car lengths, so its definitly worth it.