Well from one total newbee car shooter to another I'll take a swing at it. In the first shot what are you after? Is it supposed to be an artzy shot with the eye drawn to the reflection in the door? The camera is focused is on the wheel so what jumps out at me is the flash reflecting off the wheel and the tree reflection in the wheel arch. I think it would look better if the 5.0 was the focus point as that is the biggest contrast area and to have used no flash.
After 6 months of car shooting I've found that unless there is something special about the car or the situation it's in not very many people enjoy photos of cars except the owners of the car. So I try to go for both and shoot what the car doing what it is designed to do. Using Mustangs for an example...
And if you want to get artzy that's cool too...
So I'd like to piggy back on a suggestion above on looking at other photographers work to compare it to your own. Not this ^ junk but real automotive photographers and I have some I'd like to share with you.
1.
Camden Thrasher- Far and away my favorite, Camden has an amazing eye for capturing more than just cars, but the whole picture of the sport- the intense singularity of purpose of the drivers and teams, the natural beauty of the surroundings, the sense of history where it applies, the speed and motion of it all. Dig into his blog and don't miss his non-auto work, which is just as good.
2.
Julien Mahiels - A real pro, with great access to my kinds of events- sports cars and vintage. Beautiful work.
3.
Laurent Nivalle - A pervasive sense of style, which maybe infiltrates from his other topics in photography. Excellent post-production.
4.
Jeremy Cliff - Commercial photographer with varied tastes, another great body of work.
5.
Stefan Marjoram - Very much into old cars, pre-war stuff in particular. Stefan is an interesting character - an animator for Aardman and a sketch artist, who is also a buff on land-speed record cars of the past.
Just my .02 from 6 months of self taught shooting.