oh please excuse my inobservance - of course i'll give you an answer.
the hdri's are simple cloudy skies. i don't know of any specific name, i once renamed the .hdr's to my preferences - since then their names are sky0012.hdr and sky0023.hdr dunno if this will help you..
oh yeah ! Ilove this car, and the model is very smooth
and you'r fast ! interesting how will u be making those side mirrors cuz I had a Lot problems in making them in correct shape.
here's mine in case it's interesting