I googled.... and found this

"Was a derogatory term once used to compare these so-called Muscle cars to Japanese imports with no more then 6 cyclinders.

Now a term used to describe cars that are modified to look fast, but arn't...

Billy Bob - 'Hey Cletus...what you think this imported shitbox on wheels is running on...what with no more then 6 cyclinders?'

Cletus - 'Probabli on rice...knowing thoes yellow bastards' ""