Finally I got the Cupertino and I did it the following way:
Definitely the "cvaradd timescale -0.5" DOES NOT work with the Rage updated version. So I reinstalled the original version and then I made the console work as specified in these forums. Then I tried and definitely the cars are slolwed down. But since I am ABSOLUTELY no good in these timing-car-racing idiocies I made it even slower by changing the -0.5 to -0.2 !!! After the seconde trial I finally got my damned Cupertino and I can continue with the game. (use the 'Q' key to destroy the cars that are ahead of you and that almost gurantees success).
Goddamn it people, if you cant race then just use the console cvars: "cvaradd vehicle_boostMPH 300" - or bigger number to increase boost speed "cvaradd vehicle_god 1" for vehicle god mode "cvaradd vehicle_infiniteboost 1" - no comment needed and if you're slow to react, use: "cvaradd timescale -0.5" for 2x slowmo