To start with, it's generally best not to tell people that they're your favorite pictures as some are inclined to be more kind in their comments because of that fact. I however have no such inhibitions.
C&C per req:
1. Good composition, but the image is spoiled by two things: (1) The excessive depth of field rendering the background sharply focused and thus distracting, and (2) the reflections on the car's hoods. The use of a much larger aperture would have prevented the former, and a polarizing filter the secondary. I would also consider cropping 1/4 to 1/3 off of the top of the image.
2. The motion blur in this one appears very synthetic; may I assume this is courtesty of post-processing? Again the reflections are distracting, but less so than the previous image. In this one, I would suggest cropping everything above the background fence. Here the composition might have been improved had you been able to capture the car a little further into the track, and not right on the edge.
Overall, nice images, good subject matter, and well captured.
Just my $00.02 worth - your mileage may vary.
~John