Boyesen WPK-32AB Supercooler Black Water Pump Kit Fits: Yamaha YZ250 1999-2008 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