200mph = 322km/h
The 1972 Chrysler VH Valiant Charger R/T
is free to purchase from the autoshow. Once you get hold of it, upgrade it as much as you can, or alternatively you can download my tune to save some time (search for "Wyyvern" in the creator bar).
Once you leave the autoshow, make your way to the point in the video below (on the Jurassic Jungle curve) and head north under the dinosaur. Go flat out across the straight road, and you should be over 200mph once you reach the speedtrap.Beanpotter
pointed out that 80 medals are required to unlock the speedtrap, but Alehldean
also said you can skip this requirement by launching a private online freeroam session, the speedtrap will be present there regardless of the medal count.