Might as well buy the pro-flow kit w/k+n filter. Is 99.99 most places, have seen it for 89.99 though. In Dirt Wheels about 7-8 months back they did a pipe shootout for the yfz450. Before they started, they removed just the lid on airbox and jetted accordingly, then they dyno'd it. W/just the lid removed made 1 horsepower improvement. Not bad for just removing the lid.