stock car vs racing car

stock car and racing car both are nouns.

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

As nouns, racing car is a hypernym of stock car; that is, racing 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
racing car: a fast car that competes in races

Other hypernyms of stock car include race car, racer.

stock car (noun)	racing 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