Editing Ford GT40 (section)

=== Mk IV ===
[[File:1967 GT40 Mk IV at 2010 Canadian International AutoShow.JPG|thumb|left|1967 Ford GT40 Mk IV. This particular car, J-4, won the 1967 [[12 Hours of Sebring]].]]

In an effort to develop a car with better [[aerodynamics]] (potentially resulting in superior control and speed compared to competitors), the decision was made{{when|date=August 2024}} to re-conceptualize and redesign everything about the vehicle other than its 7-liter engine. This became the  Mk IV.<ref name="supercars.net">{{cite web|url=http://www.supercars.net/cars/694.html|title=1967 Ford GT40 Mark IV|access-date=2010-02-23|work=supercars.net}}</ref>

{{clarify span|text=In order to bring the car into alignment with Ford's "in house" ideology at the time,|reason=What is this word salad trying to say? *Specifically*.  And concisely.|date=August 2024}} more restrictive partnerships were implemented with English firms.  This resulted in the sale of Ford Advanced Vehicles to [[John Wyer]], ultimately leading to a new vehicle which would be slated for design by Ford's studios and produced by Ford's subsidiary Kar-Kraft under [[Ed Hull]]. Furthermore, there was also a partnership with the [[Brunswick Aircraft Corporation]] for expertise on the novel use of [[aluminium]] [[Honeycomb structure|honeycomb]] panels bonded together to form a lightweight, rigid "tub".

The nickname "J-car" came from its construction to meet the new Appendix J regulations<ref>{{cite web|url=http://www.ultimatecarpage.com/car/3406/Ford-Mk-IV.html|title=Ford Mk IV|access-date=22 February 2010}}</ref> introduced by the FIA in 1966;<ref>{{cite web|url=http://www.fia.com/resources/documents/2102817986__Hist_App_J_69_Art_252_a.pdf|title=Appendix J to the International Sporting Code|access-date=23 February 2010|archive-url=https://web.archive.org/web/20050302205843/http://www.fia.com/resources/documents/2102817986__Hist_App_J_69_Art_252_a.pdf|archive-date=2 March 2005|url-status=dead|df=dmy-all}}</ref> the redesign resulted in the abandonment of the original Mk I/Mk II chassis.

The first J-car was completed in March 1966 and set the fastest time at the Le Mans trials that year. The tub weighed only {{convert|86|lb|abbr=on}}, and the entire car weighed only {{convert|2660|lb|abbr=on|0}}, {{convert|300|lb|abbr=on|0}} less than the Mk II. In spite of this, it was decided to run the Mk IIs due to their proven reliability, and little or no development was done on the J-car for the rest of the season. Following Le Mans, the development program for the J-car was resumed, and a second car was built. During a test session at [[Riverside International Raceway]] in August 1966 with [[Ken Miles]] driving, the car suddenly went out of control at the end of its high-speed, {{convert|1|mi|km|adj=mid|-long|spell=in}} back straight. The honeycomb chassis shattered upon impact, and the car burst into flames, killing Miles.<ref name=stpcrk>{{cite news |url=https://news.google.com/newspapers?id=8l4xAAAAIBAJ&sjid=UHQDAAAAIBAJ&pg=3679%2C4254231 |work=St. Petersburg Times |location=(Florida) |agency=UPI |title=Crash kills ace driver Ken Miles |date=August 18, 1966 |page=1C}}</ref><ref name=dbmjapdir>{{cite news |url=https://news.google.com/newspapers?id=qZotAAAAIBAJ&sjid=vZ4FAAAAIBAJ&pg=3488%2C3514531 |work=Daytona Beach Morning Journal |location=(Florida) |agency=Associated Press |title=Miles dies in crash |date=August 18, 1966 |page=25}}</ref> It was determined that the unique, flat-topped "bread van" aerodynamics of the car, lacking any sort of spoiler, led to excess lift. Therefore, a conventional but significantly more aerodynamic body was designed.<ref name="supercars.net"/> A total of nine cars were constructed with J-car specification chassis, with six designated as Mk IVs and one as the G7A.<ref name=isr />