1
general::
Phrase(s): Give it the gun. [and] Give her the gun.
Fig. to make a motor or engine run faster; to rev up an engine. (The her is often pronounced "er.") • Bill: How fast will this thing go? Bob: I’ll give it the gun and see. • Hurry up, driver. Give ’er the gun. I’ve got to get there immediately.
McGrawhill's American Idioms And Phrasal Verbs