3406 Fuel Manifold Cover
The high pressure fuel that exits through the spill ports goes through the hollow dowel into the fuel manifold and hits the cover plate.
These highly pressurized fuel pressure pulses cause polish spots that are lined up with the spill ports on the manifold cover plate of the 3406B/C fuel system.
3306 Fuel Manifold Cover
On the 3300 series engines, a spring steel pulse deflector is provided in the fuel manifold. This protects the aluminum manifold cover from the force of the released fuel pressure pulses.