Although not strictly a GTO, a 1964 389cid Tempest did compete in the 1971 US Trans-Am series and nearly caused a sensational upset at the opening round held in pouring rain. The unsponsored car, although then six years old, was built by brilliant GM suspension engineer Herb Adams (it was his wife's old car!) and a couple of young GM engineers as a backyard project. They de-stroked the 389 to 303cid to meet the 5.0 litre class limit and cleverly tweaked the suspension so that it was superb in the wet. Bob Tullius started rear of grid and came storming through the field to be challenging Mark Donahue's works Javelin for the race lead! Sadly the Tempest's engine blew a head gasket and it failed to finish, but the legend of the 'Gray Ghost' was born. Amazing story.