well on the first image you have too much contrast and if you used photomatix to make up your hdr I would back off the black slider. Also your background enviroment is blown out I mean the sky looks like yoohoo then it looks like the warden shined his spotlight dead center over the passenger side. For being a 1st timer I don't think its that bad but sometimes hdr is supposed to be realistic to sometimes border realistic where it looks kind of like a painting enhanced image if you are looking for the grunge effect.
The 2nd image is going for grunge but it has been over processed aka cooked your whites are blown out again.
to help you get an idea have a look at some of these I found online
9 Great HDR Car Photos
your images just need to be tweaked and some corrections need to be made but hey
your getting there.The goal is to get the most details and the most range out of your images
now a days mostly all new hdr's are going to realistic look to it and the grunge effect is pretty much leaving out the door
with some exeptions that work well. As for me it depends on the image final presentation I have seen some great grunge looking
HDR.But I do prefer seeing something closer to what my eyes see everyday. I mean nobody looks outside and see's the world in chocolate unless they are color blind perhaps or they are willy wonka and the car is made out of milk chocolate.<< Sorry just felt like
cracking some jokes here. Don't take me serious.