Editing Ford GT40 (section)

=== Racing ===
[[File:Winner at Le Mans (53535080453) (cropped).jpg|thumb|Ford GT40 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, gearbox, some suspension parts and the brakes from the Mk II, the Mk IV was totally different from other GT40s, using a specific, all-new chassis and bodywork. It was undoubtedly the most radical and American variant of all the GT40s over the years. 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 the roll cage was so heavy that it negated most of the weight saving of the then-highly advanced, radically innovative honeycomb-panel construction. The Mk IV had a long, streamlined shape, which gave it exceptional top speed, crucial to do well at Le Mans (a circuit made up predominantly of straight roads connecting tight corners)—the race it was ultimately built for. A 2-speed automatic gearbox was tried, but during the extensive testing of the J-car chassis in 1966 and 1967, it was decided that the 4-speed from the Mk II would be retained.

In 1966 and early 1967, Ford's R&D department in Detroit developed a test rig to simulate circuit laps; the rig was programmed to accurately mimic the characteristics of the target circuit. The Mk IV design was revised based on weeks of simulated Le Mans laps. This was an early example of the now-common practice of using test rigs for Formula One and Le Mans vehicle protoyping.<ref>{{Cite web |title=Ford v Ferrari: The Untold Story that Saved Ford's Race |url=https://www.caranddriver.com/features/a29790131/ford-v-ferrari-mose-nowland/ |archive-url=http://web.archive.org/web/20230306213644/https://www.caranddriver.com/features/a29790131/ford-v-ferrari-mose-nowland/ |archive-date=2023-03-06 |access-date=2025-04-28 |website=www.caranddriver.com |language=en-us}}</ref>

Thanks to its streamlined aerodynamics, the car proved to be fastest in the field at Le Mans in 1967, achieving 213&nbsp;mph on the 3.6-mile [[Mulsanne Straight]].

Dan Gurney, who was 6 feet 4 inches tall, requested a bubble-shaped bodywork extension over the driver's seat to accommodate him. Gurney also complained about the weight of the Mk IV, which was {{convert|600|lb}} more than the Ferrari 330 P4, and, combined with its higher speed, put more stress on its brakes. During practice at Le Mans in 1967, in an effort to preserve the brakes, Gurney developed a strategy (also adopted by co-driver [[A.J. Foyt]] who had just won the [[1967 Indianapolis 500]]) 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 mistaken speculation within the Ford team that Gurney and Foyt, in an effort to compromise on chassis settings, had hopelessly "dialed out" their car - despite Gurney having been the fastest GT40 pilot in the 1966 practice and race. Also, Gurney was developing his own Eagle V12 F1 car with which he would win the [[1967 Belgian Grand Prix]] the very next weekend.

The Mk IV ran in only two races, the April [[1967 12 Hours of Sebring]] and the June [[1967 24 Hours of Le Mans]], and won both events. Only one Mk IV was completed for Sebring; the pressure from Ford had been increased considerably after Ford's humiliation at the [[1967 24 Hours of Daytona|1967 Daytona 24h]] in early February, when Ferrari staged a 1-2-3 finish, honored later by naming a road car the [[Ferrari Daytona]]. [[Mario Andretti]] and [[Bruce McLaren]] won Sebring, Dan Gurney and A. J. Foyt won Le Mans (their car was the Mk IV that was apparently least likely to win),{{according to whom|date=August 2024}}{{why|date=August 2024}} where the Ford-representing Shelby-American and Holman & Moody teams showed up to Le Mans with 2 Mk IVs each.<ref name="supercars.net" /> The installation of the roll cage was ultimately credited by many with saving the life of Andretti, who crashed violently at the Esses during the 1967 Le Mans yet escaped with minor injuries. Gurney later described the Mk IV as "''half-way between a road-legal passenger car and a race car; it was reliable and comfortable, but heavy''".<ref>{{cite web | url=https://www.youtube.com/watch?v=A6Kj3n-NDt0 | title='Behind the Headlights' the story of the Ford GT40 | website=[[YouTube]] | date=11 February 2019 }}</ref>

Unlike the earlier Mk I - III cars, the chassis of which were built in Britain, the Mk IV car was built entirely in the United States by Kar Kraft, Ford's performance division in [[Detroit]]. Thus, Le Mans 1967 still remains both the only all-American victory in Le Mans history — American drivers ([[Dan Gurney]] and [[A. J. Foyt]]), team ([[Carroll Shelby International|Shelby-American Inc.]]), chassis constructor ([[Ford Motor Company|Ford]]), engine manufacturer (Ford), and tires ([[Goodyear Tire and Rubber Company|Goodyear]]) — as well as the only victory of a car designed and built entirely (both chassis and engine) in the United States. A total of six Mk IVs were constructed.<ref name=isr />

One of the Mk IVs was rebuilt to [[Group 7 (motorsport)]] rules as the [[Ford G7]] in 1968, and used in the [[Can-Am]] series for 1969 and 1970, but with no success.<ref name=isr />
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