The special aluminum pcs that surround the engine are screwed to the aluminum tabs. This gives the engine compartment a nice tight seal to keep the hot air under the engine and the nice cool incoming air on the top side. See the pic below, the tabs are under the surround pcs. where you see the screws. It is a very well made setup. The type 4 sells the surrounding pcs to fit regular type 1 compartments and a special set just for the Speedster replica's.