Nice shots mate.
Number 1 could maybe do with somemore saturation. That orange/red on the HRT is really bright in real life, so could do with some pumping up. Image seems nice and sharp where it needs to be. Something you should try to take into account (when you can) are the reflections. Shooting into the sun (even on cloudy days) gives that reflection off the bonnet/windscreen. I know it's picky, but thats why you posted I gather.
Number 2 is a good panning image, but i would be inclined to have it cropped to have more empty space in front of the car, rather than behind it. It gives the illusion of the car going somewhere.
Number 3 is good. I like the frasntic pace of it, while the drivers helmet is sharp. It could do with more sat/contrast though.
Number 4 is a nice image, great light and fantastic background. My only beef with it is the large area of empty space to the left of the image. The image would have been better served using a focal point to the left in the view finder, and having the empty space to the right of the car, again, giving it somewhere to travel into. You would still have go the background you have, and the shot would appear more balanced.
They look good though. I havent shot at P.I. yet, maybe one day!