Lenhartsville, PA Boyesen Engineering has now introduced the NEW Power X-Wing, which increases horsepower and torque on 2 and 4 stroke bikes. On 2 strokes, the PowerWing improves power from idle to midrange with no loss on the top end. 4 strokes see power boosts from idle through over-rev. The Boyesen Power X-Wing simply out performs all other carburetor dividers on the market today. Motocross.comRating: "9", for the price, we would recommend anyone purchase this product if they are looking for an inexpensive way to improve the power of their big 4-stroke". Fits: Yamaha WR450F 2007-2011 YZ450F 2007-2009