What is the plastic box (an expansion chamber?) right in the middle of the engine that connects to the air input? Embossed into the plastic is "6.6L Turbo Diesel". What is the box, what does it do?

Thanks.

It is a resonating Chamber for the intake. it is supposed to quite down the Turbo Noise to... they do crack some times and let raw air in to the system. spent $2 @ home depot for a quick cap and remove the resonator and cap it. a little louder turbo whine which always sounds good but you dont risk raw unfiltered air in your motor....