What car do you need for "Drive 500 mls in a Timesless Super car? thanks
Start your own multiplayer lobby, set the car body family to ‘Timeless Supercar’, and then Select car and Buy car. This will show you which ones you can use for that challenge.
FM5 Game FAQ link: How do I see my car’s Body Family for eligibility in Career, Rivals, Multiplayer hoppers, or Challenges?
Also, please remember to search for your subject to find existing threads that may answer your question rather than creating new duplicate threads on the same topic:
http://forums.forza.net/turn10_search.aspx?search=timeless