NASCAR Racing: Number of cars?, nascar champion, uproar

Question
Why is there 43 cars per race? Who chose the number and why 43?

Answer
Sorry for the delay in the answer, I was out of town over the weekend. Why 43 cars?
I call it the Richard Petty rule. The field kept getting expanded until it eventually reached 42 cars. As the King's career wound down all of a sudden he was having trouble making the field. The Petty fans were in an uproar and began staying home (this was prior to "sold-out" races) when he didn't make the race. So NASCAR added the "Past Champion" provisional, a way to get RP in the field and keep the fans coming to the race.
The 43rd position could be awarded to any past NASCAR champion that didn't make it into the race on qualifying with that position going to the next fastest qualifier that didn't make the field if all past champions made the race.
Nowadays it's just never been changed from 43.