Windage is the flow of air within the crankcase. Each time a piston comes down in the cylinder bore the air under it is pushed into the crank area and each time the piston goes up the air is being pulled behind it. At the same time the rotating assembly is spinning and churning the air and adding oil into the mix. The windage tray keeps the windage around the crank from the oil in the sump area. It allows the oil coming off the crank to easily enter the sump without the windage affecting the scavenging of oil already in the sump. The windage tray also keeps any oil in the sump from getting into the rotating assembly during vehicle motion.