Wiktionary
give it the gun
vb. 1 (&lit give it gun English) 2 (context idiomatic English) To cause a specific vehicle to accelerate; to open the throttle of an engine.
Usage examples of "give it the gun".
The Zil was on the move but the surface was tricky and I had to keep tapping the throttle to use the power of the huge engine to take me in a series of swings before I could straighten up and give it the gun.