Shelf or no shelf? It's fairly big bucks to machine off the cast-in manifold on a Cummins 24-V and make/buy a new manifold. When you are grasping for every horse it can reap enough rewards to make it worthwhile, but it still ain't cheap. The main gain is the ability to be able to improve the intake ports, particularly #1 and #6, which need the most help. Gavin Knisely gave us some informal numbers of a top-quality job with the shelf on and one with the shelf off. With the flow bench results he presented, it shows around a 21-percent difference. The main difference is the ability to thoroughly work over the intake ports. The shelf itself isn't the major flow impediment, though removing it and replacing it with a custom intake is worth some flow and power. The plate shown here in front is the mounting flange for a new manifold to be constructed. None of the mounting bolt holes have been drilled and tapped at this point. Knisely also used this as a template to match the ports.