Fits GM V8, GM V6, Ford 260-302, 351W. Anodized aluminum restrictor plates are mounted under the water outlet on the intake manifold. By reducing the outlet flow of the engine block the cooling water can absorb greater amount of heat, which results in improving cooling. Kit consists of three restrictor plates with 5/8", 3/4", and 1" ID holes (2 1/8" OD), one of which should suit the particular application.