This is the CNC ported version of the S&S cast aluminum manifold that fits all 55mm throttle bodies and works excellent with factory as well as ported heads. Porting is done using a 5-Axis CNC machining center for the ultimate in consistent shape and flow characteristics. Understanding polished porting has little impact on the intake side, S&S leverages a uniformly spaced and shaped texture that not only creates a larger surface area to encourage fuel dissipation but also superior atomization of the fuel-air mixture. A must-have for top-level performance of Big Bore Monster Milwaukee Eight.