One of my pet peeves when shooting at car shows is people getting in the shot. Occasionally having a person candidly placed in the frame with a vehicle adds to the overall shot but, more often than not it's a distraction that takes away from the subject. I understand that it's a car show so the attending crowd will be a mixed bag of spectators, enthusiasts, photographers, kids and even pets. There are a few ways to handle this. You could patiently wait on the crowd to dwindle, If possible early access works well or as a last resort you could always be that guy who speaks loudly asking people to move....dont be that guy.
In the photo above you'll see how I was able to use the magical powers of photoshop to remove the unwanted objects and make the shot usable. I spent a great deal of time cloning to get it right. I have to tell you that I am far from mastering photoshop in fact, I learn something new and become a more proficient user everytime I use it.
If you havent already seen the entire set look here Rauh-Welt Begriff