petrol engine vs inlet manifold

petrol engine and inlet manifold both are nouns.

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

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