Nice pics mate.
I always find it a mega pain in the arse photographing black cars, with or without a polarising filter.
Circular Polariser ought not to make a massive difference as the biggest issue you've got with a black car (and things like grey tarmac, silver wheels, glass, blue skies, etc) is the contrast and the camera's metering of the light reflecting off the different colours of the subject. I always struggled to photograph my State Blue (ie metallic navy) Focus but find the wife's Steel Grey Golf and my silver Octavia much easier.
