If you mean like what it's chassis or whatever is based on, i don't know. But it's not supposed to be a real car. Wikipedia says that the only car that closly resembles the Mach 5 is an early Chaparral. This one person made a real Mach 5 based on a Corvette.
http://www.sussexcountyonline.com/news/columns/cars/carreviews/speedracer.html