Aton, you should add all the vray elements which are present in your scene. If its just cars you would probably need.
Diffuse
RawGI
Raw Lighting
Relection
Refraction
Specular
zdepth
Multiply the diffuse with both the gi and lighting then add everything else together. I don't use after effects so cant help you with that. I would make all your lights in the scene white and change the colour in your comp too.
You will also need a shadow pass, create another instance of your cars and make them not visible to camera, then make your ground a vray matte with -1 on alpha, check shadows option. I would recommend investing in RPmanager if you are doing lots of jobs like this, it will save you lots of headaches!
The chaosgroup forum has more users who do this kind of thing. try posting there too.