I just finished with the install of a K&N 77 Series High-Flow Performance Kit on my X. The differences are like night and day! The engine now breaths so much more efficiently, and it produces quite the attractive breath when you punch it. If you thought the engine was loud when accelearating before, install one of these and it's like Nascar. I would highly recommend this aftermarket upgrade, one of only a few to boast the already powerful engine. I purchased mine from eBay fo $240.