I might have a few good backgrounds for ya:

1: http://img690.imageshack.us/i/14555265.jpg/
2: http://img28.imageshack.us/i/opelastragtc20051024x76.jpg/
3: http://img696.imageshack.us/i/16056391.jpg/

maybe they are usefull

Tnx a lot Pipo! I've found wheels tonight I've to work

Tonight lot of work done not yet finished but at the moment I'm satisfied

The rear wheel is off and not sure why I feel the chop is kinda too simple.

Fixed rear wheel (tnx)... my chops usually are not so complicated, I prefer something that can be reproduced in the reality (except the 500 Koenigsegg ). Another update:

That's one wide inter-cooler for such a small car.

Interior needs some work. See how the seats are so visible in there but nothing else is? We should be able to see the other sides of the window pillars and through the windows to the background.

Side exhaust needs to be redone too because now it looks like a rectangular sticker with a white rectangle outline in it. If it was your intent for it to actually be a sticker, pay no mind to this.

Roll bar tubes would look a lot better if they were thicker. The current ones are about the same thickness as you would find on the climbing contraptions at a children's playground.

I would also suggest creating a subtle front wing for the front bumper. Looks so naked without one with the bumper hole being that close to the ground.

Tnx Ollite
No the side exhaust is not a sticker ... not yet
For interios and roll-bar I try to fix all, is the first time I try to chop an interior (also first time for matte paint)
For the front bumper... mmmh ok I try also for this one

The wheels still seemed off to me, maybe you should make them in the same wide as the rear is wider than the front now. And, the rear arch should have the same lighting as the front imo.

Interiors fixed with windows, new roll bar... now time for dashboard and steering wheel

Same pic with some post production in Photoshop: