NASCAR Racing: Engine changes after qualifying, engine changes, cars

Question
What are the rules regarding changing the cars engine after qualifying in both impound and non impound races? Was there ever a time when teams had special qualifying engines that they changed after qualifying?
Thanks,
Danny

Answer
Rules for changing engines are simple. If you change your engine after qualifying, you lose your qualifying position and start in the back of the field. As for a qualifying engine, yes I think they made it a one engine per weekend in 2001 or 2002, but they used to have it where you would qualify with a certain engine and then change to another engine for the race.