pal vs pal up

pal is a noun but pal up is not a noun.

Word	Noun	Adjective	Verb	Adverb
pal	Yes	No	Yes	No
pal up	No	No	Yes	No

As verbs, pal and pal up are synonyms defined as:

Other synonyms of pal include chum up.

pal (noun)	pal up (noun)
a close friend who accompanies his buddies in their activities

pal (verb)	pal up (verb)
become friends; act friendly towards	become friends; act friendly towards