You need to increase the render sample amount. Maybe reduce the calculation-box size (forgot the proper name) from 256x256 to 64x64.
If you want a lighting setup as in your mockup, then you will need to have a small emitter plane pushing light towards the nose (alternately - a large topside plane casting downwards placed way in front of the car), a plane illuminating the underside and a thin emission strip running the back wall.
You’ll also have to tweak the materials’ glossy roughness up for that softer look.
Suggest you put the world material down to black and set up some walls/slopes to cover the backdrop of the render - right now, it seems that the global world light is washing out some shadows.
There’s a spot-on car rendering tutorial that you should check out, if you haven’t (http://www.youtube.com/watch?v=dkgjxo2fPBo), it will help a lot in figuring out just what cycles does with all the materials and world stuffs.