Many people shoot car shows with a wide-angle, so switching to a telephoto can make your images stand out. The trouble is you need patience to use a telephoto at an event or show, and you need to get used to sitting tight and waiting for your moment.
Focus on the details and people too rather than just generic shots of every car slap bang in the middle of the frame. And use the elements around you as compositional aids – frame subjects between other cars, or through windows. Use reflections and lead-in lines to your advance too. Shooting past or through things can add depth and dimensionality.