Apologies to Tonystew42... Stepped away from my PC for a while, didnt hit refresh...
1) 7.5/10 - I Like the fact that you used Karts, there seems to be a lack of them on the boards

. The Compo is good, could've maybe benefitted from a different shutter speed and aperture to enhance the sense of speed, the exposure could maybe be brought down a touch to help saturate the colours more (or use photoshop)
2) 7.5/10 - I really like this image, the drive has a "What you looking at" stare going on, the only thing is that its too dark (for me anyway)
3) 8.5/10 - I Like the B&W treatment here, could've probably used a slower shutter speed to accentuate the loss of control on the spin. Overall i like it
4) 6/10 I dont think the B&W works too well here, it looks a little muted and lacks contrast, there is also no sense of speed in the shot, they almost look as if they are parked
Hope that was helpful for both posts, tried to be as constructive as i could