Boyesen WPK-38B Supercooler Black Water Pump Kit Fits: Yamaha YZ/WR426F 00-02, WR450F 03-15, YZ450F 03-09, YFZ450 04-09 &amp; 12-13 By casting a totally new water pump cover, Boyesen was able to maximize the flow through the unit; Boyesen's design takes advantage of everything from Bernoulli's effect to biological studies Unlike the stocker, Boyesen's water inlet has an increasing diameter and artfully curved shape; this is a vast improvement over most stock inlets, which decrease in diameter as they near the impeller and have a 90-degree bend at the pump Patented nautilus style impeller for hydrodynamic efficiency, reducing heat, gaining horsepower and extending engine life Asbestos-free gasket is bound with nitrile for tight, leak-free seal