race car vs racer

race car and racer both are nouns.

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

As nouns, race car and racer are synonyms defined as:

Other synonyms of race car include racing car.

race car (noun)	racer (noun)
a fast car that competes in races	an animal that races
	slender fast-moving North American snakes
	a fast car that competes in races
	someone who drives racing cars at high speeds