Small Block Chevy versions of these intake manifolds are engineered specifically to port match fit RHS? 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 applications up 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. FAST? also offers a port fuel injection version of these manifolds. Unlike the competition, the EFI manifold features port angle optimized injector bung mounting and machining features. FAST? engineers laid the injectors down on an angle that points injectors directly at the valve stem. Additionally, the EFI manifold features integral sensors improving function, fitment and packaging. This is the only 4BBL-type EFI manifold on the market with an integral idle air control circuit.