Answer: soupup

AnswerCrossword Clue
SOUPUP

Improve, slangily

SOUPUP

Improve, as a motor

SOUPUP

Enliven

SOUPUP
Increase the power of, as an engine
SOUPUP
Add horsepower
SOUPUPAdd juice to, as an engine: 2 wds.
SOUPUPMake more awesome, as a car
SOUPUPImprove a muscle car engine
SOUPUPGoose the auto engine
SOUPUPMake more powerful