Wow. Pretty good for a first shot.
He looks a little small for the shell in Bot mode--just the proportion of parts to the body I think. You might want to work out some kind of hinge-concept for allowing the arms to come out more fully. Something that swings those parts of the car around the wheel well out of the way. (perhaps towards his back) Otherwise, I quite like it.
EDIT: And I had a concept for what to do. Perhaps take the wheel-well sections and 'gullwing' them in robot mode, but have their be some hidden rocket launchers under them that would then sit on his shoulders. That way you have room for the arms, and the 'kibble' would have purpose.
I know, this is coming from someone who couldn't reshell an Alt. to save his life. Still, I had to put it out there.