Why does nascar line up with 43 cars and not 42 or 44?

May be...

Well if it were 42 you'd be asking why not 41 or 43

They figured that was the MAXIMUM # of cars they could cram onto the smaller tracks and pit stalls.

and for the sake of continuity
that became the limit for all tracks.

"In the past field size was based on the size of the tracks. At one time there was over 50 drivers running at tracks like Daytona and as little as 28 running at tracks like Hickory. However, when the modern era came about and the Money got better with Winston as the series sponsor NASCAR and the drivers settled on 42 drivers for the field, as most tracks would accomodiate that many pit stalls.

Again, keep in mind NASCAR used to have up to 60 cars trying to make the field and if you could get in then you could make money.

In 1989, the King Richard Petty, failed to qualify for a Race, So 3 time Champion Darrell Waltrip, who has been know to shoot his mouth off, told a national audience that it was a shame someone with the Kings status should miss a race. So Darrell proposed a "Past Champions" provisional that would allow any previous champion to be placed in the 43rd starting spot.
Well in 1998, I believe, NASCAR decided to make the 43rd spot perminate. So if a past champions provisional was not used then the 43rd spot would be fielded by the next highest qualifier."

http://wiki.answers.com/Q/Why_do_43_cars...

It's all here.

http://www.nascar.com/2002/news/headline...

because every track has only 43 pit stalls in the pits.

It has varied a great deal over the years..
At the beginning they put everyone that showed up, on the track..
By the seventies they had it down to thirty cars for a short track
(under a mile), and forty two for speedways, and super speedways..
I believe the forty third spot (past Champions provisional) was added
in the eighties, as well as the rest of the forty three on short tracks..washington post mini page