[Morley]

You mean the plenum is hot? Plenum is the upper part with the runners going down to the base which is the intake manifold.
The plenum is always hot for a very simple reason....convection. Heat rises AND aluminum is a very good conductor of heat.
Believe it or not, the inside of the plenum is no where near the temp of the outside since aluminum conducts heat so well. Also, the plenum isn't all that hot when you are moving and the engine is running, but when you stop and shut down, all of that cooling air flow in the engine bay is gone as is the cool air going down the plenum. Since the aluminum intake, runners & plenum sit on top of a cast iron block, they suck the heat from the iron quickly.