Car modified for extra power and speed (3,3)
I believe the answer is:
hot rod
'car modified for extra power and speed' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for hot rod that I've seen before include "Car with souped-up engine" , "Car modified for extra power and speed" , "Souped-up vehicle" , "Car modified to increase speed and acceleration" , "fast vehicle" .)