I agree with Rhino about the cropping. Other things:
1. The tubing/chair or whatever it is distracts from the car, maybe move any stuff like that out of the shot
2. Consider using flash in such as pic 6 to light up the car but keep the background darkish with the dramatic colours
3. Also on pic 6, consider shooting from a lower angle to get your car outlined against the sky
4. I'm not a fan of obviously HDR'd pics
Good pics for your first shoot though and a nice location too.