The stock air cleaner is restrictive in that it is designed to muffle the sound of the incoming air as well as make sure that water has a harder time of entering the engine. Anything you can do to let the air in is a bonus. Your engine will like you. I, personally, have the so-called 'muscle cover' from S&S and I can report that the engine responds faster, is much happier at all speeds but is now more vocal than ever.
Much of this is due in large part to limiting the noise emissions that the EPA in the United States enacted. This is a loud engine.
