Charlie: there is virtually NO affordable sound technology currently available which can be heard completely over the roar of race car engines at "full-song". The best race track sound systems I've ever had the privilege to announced on were: Daytona (obviously), Iowa Speedway and Williams Grove Speedway. Even those were drowned out by the sound of cars in competition--I'm sure there are others out there which may come close. The biggest hurdles to overcome are: the size of the area needed to be covered, the number of people in attendance and the BIG problem of sound systems being considered "too loud" once the cars pass by the grandstand(s). Naturally, technology is getting better; a company called Community Sound is probably the industry leader in designing and engineering of sound technology for large venues, but their best systems are HUGELY expensive (as one might expect!). One of the biggest hurdles to overcome is a system which could be loud enough while the cars roar by BUT won't be excruciatingly loud once the cars get further away from the grandstand(s) and things get relatively quiet. Interestingly enough, Williams Grove (unless they have changed it!) relied on proven old-school technology. Their speakers were (are) the old Altec-Lansing Public Address fairground style dish shaped 18" (or larger in diameter) horns, pretty impressive despite their age!
Drag racing and road course layouts present HUGE, unique challenges of their own. It is doubtful that ANY system could be designed to overcome nitro-powered Top Dragsters and Funny Cars. Again, they would be agonizingly too loud once the cars passed by! More than likely road courses (like Watkins Glen) present even tougher challenges, depending on the actual track distance of the course.
There is always the high likelihood of "dead-spots" produced by any system and that annoying "echo" produced by any system. In discussions I enjoyed having with Daytona's engineer (Isaac Addison) and others, one thing they all agreed upon was: that the best "coverage" for a system is to install several speakers in tandem, pointed in the direct area of where the sound system needed to be heard. Some call it and other designs "zoning".
But WAIT, some might say, what about the sound system design of large music concert performances? Then you're talking astronomical costs; certainly impossible for nearly any local track to heavily invest in. In short, there are very few solutions available at reasonable expense.
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