You can see the process they went through.....
"we'll replace the restrictive inlet manifold with a cast plenum and four inlet manifold runners with the throttle bolted on one end".
er,aka what Vauxhall would have fitted it with had they not had to strangle it.
Then they thought "what shall we call it?".
"inlet manifold", er, "replacement inlet manifold", er "uprated intake box", er , "high flow inlet" , er, I know! "powerbox". Yeah.