The most common and most likely answer to this crossword clue is the 6 letter word HOTROD
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Buddy explains!
The straight part
We know that "souped-up car" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case souped-up car = hotrod.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 HOTROD mean?
HOTROD noun- Typically a passenger vehicle modified to run and/or accelerate faster. The term may be used generically to apply to any car, truck, or motorcycle (et al.) modified for increased speed and/or performance. It may also be used to specifically describe and refer to modified cars from the original (or traditional) era of "hot rods", post World War II and prior to 1960.
- (sexuality) The penis.