The RHS23 Aluminum Intake Manifolds are engineered specifically to port match fit RHS23 Small Block Chevy cylinder heads. Additionally these manifolds are the only ones designed with a 4150 flange and bolt machining to fit all versions of Small Block Chevy cylinder heads including classic originals Vortec GM heads and late model perimeter corner vertical bolt style crate engine heads. They provide the power and strong torque curve throughout the mid-RPM range that is required for performance street circle track and drag race applicationsp to 434c.i. The manifolds also feature auxiliary water ports integral water crossover and dual sided distributor mounting points. Female pipe fittings at all four corners allow external water lines for reverse cooling applications.