stock car vs race car

stock car and race car both are nouns.

Word	Noun	Adjective	Verb	Adverb
stock car	Yes	No	No	No
race car	Yes	No	No	No

As nouns, race car is a hypernym of stock car; that is, race car is a word with a broader meaning than stock car:

stock car: a racing car with the basic chassis of a commercially available car
race car: a fast car that competes in races

Other hypernyms of stock car include racer, racing car.

stock car (noun)	race car (noun)
a racing car with the basic chassis of a commercially available car	a fast car that competes in races
a car kept in dealers' stock for regular sales