Is NASCAR mainly a “white sport”? How many Black NASCAR Drivers has there ever been before. ?

I don't think it's a "Black sport" I think it's a middle class sport. I've said this before, sports appear to favour certain races/skin colours but when you look deeper, it's more economic factors than anything else. Golf is an example. It's a pricey sport. A set of Golf clubs can set you back $500, then there's the ride to the course, the fee etc. The middle/upper classes who can afford this are dominated by white people, so it's a mainly white sport.

Basketball which is a mainly "Black" sport, is mainly played in urban areas and is considerably cheaper. Most black people are at the lower end of the economic spectrum (this is thankfully changing), so higher uptake in basketball amongst black people.

To be a race driver, any form of racing, is an expensive business. Hence there being more white drivers. It's not down to race, it's economic. As more black/hispanic/asian people move up the economic ladder, the more you will see in sports like Nascar, Golf etc...