Granatelli approached Carrol Shelby with an idea too good to ignore: offer a Paxton supercharger as optional equipment on the GT350. The Granatelli family controlled the Paxton Products Division of Studebaker Corporation.

Intrigued, Shelby loaned a developmental prototype GT350 to Grantelli for the supercharger installation. The car came back from Paxton with an additional 135 horsepower, enough for the GT350 to trounce an AC Cobra in a drag race….with Granatelli and Shelby themselves doing the driving. Shelby immediately ordered the concept to be developed and put into production. The plan was not only to offer the supercharger as an option on new GT350s but also sell a complete supercharger package for over-the-counter sales.

The car pictured here, serial number 5S425, is the second Shelby/Paxton prototype, delivered new to Shelby on June 4th 1965 and then sent to Paxton Products for the supercharger installation. The car then became a promotional demonstrator before being shipped to Trudell Ford in Michgian for retail sale. Since the supercharger was removed from the first prototype 5S425 is believed to be the only 1965 GT350 to be sold with the Paxton supercharger.

Despite the huge power increase the supercharger option was not often ordered on new GT350s. Only 11 cars received the supercharger for 1966 and 35 for 1967. For 1968 the supercharger option was contemplated but never actually put into production.

5S425 is an unrestored and remarkably well preserved survivor.