For shooting cars how do you mean? Moving cars? As for stationary cars I don't recommend it without getting really creative. Cars are shiny, flashes makes their paint work look really dull. Those magazine shots often use 4+ strobes through softboxs or other diffusers. So if that's the look you are going for a different approach would probably be better.
That said the SB600 and SB800 are fantastic units as far as flashes go.