inlet manifold vs petrol engine

inlet manifold and petrol engine both are nouns.

Word	Noun	Adjective	Verb	Adverb
inlet manifold	Yes	No	No	No
petrol engine	Yes	No	No	No

inlet manifold (noun)	petrol engine (noun)
manifold that carries vaporized fuel from the carburetor to the inlet valves of the cylinders	an internal-combustion engine that burns gasoline; most automobiles are driven by gasoline engines