Manufactured by Robert Shaw and modified by Stewart, this custom thermostat features a balanced sleeve design and is constructed for high flow, high rotation per minute applications. Strongly recommended for any performance application and must be used with Stewart Stage 2, 3 or 4 water pumps. Stage 2, 3 and 4 small block Chevy water pumps do not have the factory bypass hole, therefore it features three 0.187 inch hole in the modified high flow thermostat that moves the bypass to thermostat. This also allows air to escape on initial system fill making bleeding the cooling system much easier.