If you do the maths on such a track the problem with a loop is the actual g-force to get up and over would squish a driver like a bug. Also no sanctioning body would license such a track as there would be MASSIVE safety issues regarding what happens if some poor unfortunate doesn't have enough speed to make it over the top.
Although it DOES sound cool
As for the figure 8, oh yeah, I'm assuming you want the crossover to be on the same level!!!! The marshals would LOVE you for that one
