By casting a totally new water pump cover, Boisean 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. Can reduce engine temperatures by as much as ten degrees . Fits: Yamaha YZ250F 2014-2019, WR250F & YZ250FX 2015-2019