Led by Bunkie Knudsend, who was to turn out to be a short-term Ford president, Ford brought out a series of "large platform" Mustangs that are remember mainly for their poor performance and overweight, overbloated design.

With Bunkie Knudsen and his GM cronies fully in charge of Ford, planning went ahead on the "new, improved" (read that bigger) Mustangs. The small Mustang was gone.

The charge to large, Knudsen's GM protégé Shinoda, and supported by Dave Ash and his Ford Design crew, was going to result in a series of overbloated and overweight Mustangs in 1971 (and 73 and 73).

It was reported that the 1971 "flatback", as it was termed by Car Life, Mustang was approved while Knudsen was looking at the fiberglass workup in the design studio smoking a cigar. When it was finished the resulting vehicle, which bore some resemblance to other Mustangs – long front/short deck - was much larger.

Car historian Gary Witzenburg has noted that the 1971 Mustang was approved for final build during the real heyday of the pony car. There were all kinds of competition in this arena, even from tiny American Motors that fielded a mildly successful Javelin, Pontiac and Chevy had just completed successful reworks of their popular Firebird and Camaro respectively and Pontiac inspired the larger performance vehicle with its GTO.

At the time the 1971 Mustang was approved, people didn't know the market had peaked. It was expected it to remain a growing and profitable piece of the pie. The new Mustang was Torino-based. It seemed to answer a market where buyers were still flush marketing had decided that they were craving Mustangs that were stuffed with as much as possible.

In the middle of this, Carroll Shelby had decided to drop out of the market and that definitely left a large hole in Ford's marketing plan, they answered with the Boss 351, which was to appear in 1970 and disappear after the 1971.

The 1971 Mach I and Boss 351 epitomized Ford's ultra-stylized designs. Their front ends featured a blacked-out eggcrate styling with just a single bright oval surround. The center of the surround featured a Mustang logo. The Mach I and Boss featured the unique addition of running lamps surrounding the Mustang. All Mustangs models sported steeply rake windshields and the hoods finished in cowls that hid the wipers. The hardtops featured a "flying buttress" –style rear roof quarter and shared a higher deck with the convertibles. A simple straight line high on the body defined the beltline. The roofline of the "fastback" was almost flat (a 17-degree rake).

The lineup for 1971 included the base hardtop, Grande hardtop, convertible, sportsroof (fastback), Mach I and Boss 351. The 1971 added an inch to the wheelbase (109) and it was 187 inches overall. The number of engines available was rationalized to include:

• 250 CID, 145-hp six
• 1 302 CID, 210-hp V-8
• 1 351 CID, 240-330 CID, V8
• 1 351 CID, 168-275 CID, V-8
• 1 429 CID, 375-hp, V-8

Sales that year, thanks to a mild recession, were only 149,678 – down a long way from the 600,000-plus in 1966 – and government safety, emissions and fuel economy regulations were beginning to have an effect.