ORIGINAL: dhvaughan

another way to describe it, is the intake(plenum) is a hollow keg, with the throttle body hole on top, and a removable plate forming the bottom of the keg. the removable plate is also called the belly pan. the gasket that seals the bottom plate to the intake (forming the keg) is called the plenum gasket or belly pan gasket. its airtight seal is critical for proper vacuum control. above the belly pan is supposed to be air, with strong vacuum, pulling in air through the throttle body, which is a pcm metered device. below the belly pan is supposed to be a sealed area of oil and lifters and pushrods. the mix of metals (cast iron heads, aluminum intake, and steel belly plan) is a recipe for disaster and about the stupidest of all the stupid things you run into on these trucks. the steel pan expands and contracts differently than the aluminum intake, which saws the gasket apart. the aftermarket solution, still NOT adopted by dodge, is to replace the steel pan with a thick aluminum pan that expands and contracts at the same rate. when (not if) the gasket fails, then the engine sucks unmetered air and oil into the intake, causing loss of oil, loss of power, lean condition, and pinging (spark knocking).
see pics...
https://dodgeforum.com/m_735291/tm.htm