The most common and most likely answer to this crossword clue is the 12 letter word TURBOCHARGER
I've seen this crossword clue in The Guardian
T
U
R
B
O
C
H
A
R
G
E
R
More clues leading to the result TURBOCHARGER
Buddy explains!
The straight part
We know that "extra speed with this?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case extra speed with this? = turbocharger.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TURBOCHARGER mean?
TURBOCHARGER noun- Inlet air compressor for an internal combustion engine (either Otto or Diesel cycle), powered from the exhaust air.