Hi James. Not bad shots. I'd be thinking about your compositions, I know that it's a cliche but you should keep the rule of thirds in mind for starters.
For example in number 2 I'd think about not having the headlights in the centre of the shot. I'd offset it lower and take the shot from a slightly (very slightly) higher angle. It helps give the car a more muscular stance but it also pushes the photo into a nicer balance. The background is in thirds but you aren't taking a photo of the background. Also a little bit of a straighten wouldn't hurt.
In number one I'd consider where you want your focus - I'd suggest that the headlights should be treated like someones eyes- i.e. you want them in focus as the car is the subject.
Number 3 I'd do a tighter crop and lose some of the left and side and a small amount of the bottom and possibly consider rotating clockwise into more of a dutch angle so that your lines are focussing more toward the engineer in the background.
Number 4, a tighter crop to get rid of the extraneous bits on the left. They add nothing to the photo and the car has some really nice simplicity to it - enhance that by making everything else as simple as you can.
Number 5 - wheel in the centre of the shot. I'm not a huge fan of centred views unless there is a symmetry that really calls for it, in this case I'd think about a tighter crop pushing the wheel into more of a lower right third.
Number 6 - nice shot, excellent processing, I'd just tighten the crop again to loose some of the blue car in the background.
Number 7 and 8 - not my thing really - the placement of the subjects is a bit bland and other than the text on the can I'm not really seeing where you're wanting to send the eyes of your viewers. With the wheel you've cut off the source of the wheel spokes so your eyes get led to something that is partially missing and you're left with the word 'MOTORSPORT' on the rim as the possible subject matter. If you're going for simple, then you need to be very specific about where and how you're leading the viewers eyes.
On the plus side there is nothing wrong with your processing, but I would certainly look at the rules of thirds and try to gain an understanding of using the lines in a shot to lead your viewers into the subject matter. If simplicity is your aim then try to embrace it. Remember that in all shots there is a foreground, a mid and a background and they all contribute in one way or another so before you press the shutter, try to look at the photo from a 2 dimensional composition perspective, keep the basics in mind. You can start breaking the rules later if it serves the shot but they're there for a reason. Hope this helps!