Hello, been looking everywhere and couldn't find even a little of help, until i went more deeper and found it my self
If you been looking on the Tunnels for the Fastest car , for hours as i did... Then you might enjoy seeing this short guide to save your time.

1.No the Fastest car won't be spawner here
2.No, from my research you don't have to do any Panam mission to get the car.

For me the car appeared when i reached lvl *40 Street Creed*
So you have to reach *Street Creed* lvl 40 to unlock the car automaticaly, it will appear on map as a " ! " , on the tunel, you have the car waitin for you with some gifts, and Jhony is here too for some time.
When you get closer to the car it unlock on the map, hop on it , and is forever your

Have fun. Don't forget to give me awards if it helped you , pretty please <33