Dunefool is probaly right about it being a good filter, BUT look how restrictive that screen,wire mesh holder thingie is. All I know is mine sure runs better and sounds better with the lid off and using the prodesign with k&n filter. I did slip the leg end of a old pair of pantie hose over the lid and it fits and looks great. It's like a pre pre-filter. It actualy repels water too! By the way Dunefool I went back and look at the Dynos that Dirtwheels ran on the 06 YFZ and 450r and at 6000 rpms the 450r is producing 5 more hp the the yfz. Overall it has 2.5 more hp. I'm headed out this weekend in search of some of those yfz's at the local riding area. I'll let you know how I do.[img]i/expressions/face-icon-small-happy.gif[/img]