Complex sentence: The 5.4 L used a reinforced plastic intake manifold while the Aviator 4.6 L used an aluminum variable runner length intake manifold similar in design to the FR500 magnesium intake sold through Ford Racing Performance Parts (FRPP) for the 4-valve DOHC Mustang engines.
Split into simpler sentences: The 5.4 L used a reinforced plastic intake manifold while the Aviator 4.6 L used an aluminum intake manifold with variable runner lengths. The Aviator intake manifold design is similar to the magnesium FR500 intake sold through Ford Racing Performance Parts (FRPP) for the 4-valve DOHC Mustang engines.