The Mk IV was a completely new car, not just an evolution of the Mk II. Developed from the J-Car, which was in itself a disappointment, Ford committed to make the Mk IV competitive after Ferrari scored a decisive 1-2-3 victory at Daytona in February, 1967.
On April 1 of that year the Mk IV made its race debut in the hands of the very capable pair of Mario Andretti and Bruce McLaren. Ferrari decided not to participate, but a very strong Texas team presented Ford with plenty of competition. The smart money was on Ford. Andretti gave the first indication that the racers from Dearborn would live up to expectations by being the fastest qualifier, setting a new track record in the process!
McLaren started the race in the Shelby American-entered Mk IV and engaged into an early battle with the Type 2F of Hall/Spence. At the end of hours 1 and 2, Andretti/McLaren held the lead, losing it to the Hall/Spence car at the end of hour 3, before their white car retired with transmission problems. The battle between these teams produced some exciting racing while it lasted: the lap record was broken no less than twenty times!
Despite some early excitement, the yellow #1 Mk IV scored victory with a record-setting 12-lap margin over the other factory-entered Ford; a Mk II driven by Foyt/Ruby. Moreover, Andretti/McLaren were the first to average more than 100mph over the entire 12 hours!