The Mk IV
The Mk IV was built around a reinforced J chassis powered by the same 7.0 L engine as the Mk II. Excluding the engine, the Mk IV was totally different from other GT40s, using a specific chassis and specific bodywork. As a direct result of the Miles accident, the team installed a NASCAR-style steel-tube roll cage in the Mk. IV, which made it much safer but negated most of the weight saving of the honeycomb-panel construction. Dan Gurney often complained about the weight of the Mk IV, since the car was 600 pounds heavier than the Ferraris he raced. During practice at Le Mans in 1967, in an effort to preserve the fragile brakes, Gurney developed a strategy (also adopted by co-driver A.J. Foyt) of backing completely off the throttle several hundred yards before the approach to the Mulsanne hairpin and virtually coasting into the braking area. This technique saved the brakes, but the resulting increase in the car's recorded lap times during practice led to speculation within the Ford team that Gurney and Foyt had hopelessly "dialed out" their car.
The Mk. IV ran in only two races, the 1967 12 Hours of Sebring and the 1967 24 Hours of Le Mans but won both events.[7] The installation of the roll cage was ultimately credited by many with saving the life of Mario Andretti, who crashed violently in a Mk. IV during the 1967 Le Mans, but escaped with minor injuries. Unlike the earlier Mk.I and III cars, which were entirely British, the Mk.IIs & IVs were built in America, the latter by Shelby. A total of 6 Mk IVs were constructed.[1]