Milodon's Water Outlet Restrictors replace the thermostat within the thermostat housing, in race applications. These restrictors work to slow the flow of coolant through the block and radiator which allows more heat to be absorbed from the block and more heat to be released through the radiator. In cases where the engine has excess cooling capacity, as in alcohol engines, they will provide a higher amount of restriction that what a thermostat can. Included are 1", 3/4" and 5/8" restrictors.