How does NASCAR pick a pace car?

Answer 1

Supplying the pace car is considered an honor reserved for the current four participating manufacturers', and is also a very valued advertising op, given for contributing the research, and development required to keep the sport as cutting edge as possible. The duties rotate, as to give each of the four equal time, as not to show favortism to one, or the other. I think the previous years manufacturer's cup winner gets certain races like Daytona 500, ect.

Answer 2

It rotates amongst the participating manufacturers, with exceptions being made for sponsored races.