[Christ]

Look up DPFI intake for a D15B2 engine in a Honda Civic.

I don't think I have any more of the plenums laying around.

Basically, the intake pipe intersects so that the air is forced to move in a spiral pattern through the round plenum, creating a vortex in the intake throat (whirlpool shape) that allows air to pack into the intake slightly pressurized. The piece of metal in there is to ensure that after one full turn, the spinning air doesn't mix with the incoming, instable air, defeating the whole intake setup.

If you remove it, Centrifugal force keeps the air moving outward instead of directing it into the throat, so the swirled air collides with the incoming air, making a huge restriction.

The throat is at a 90* angle to the intake pipe, which is why they made the design that way.