The 1971 model was probably the longest Mustang produced.
This was the last high-performance model because after this the general trend was towards smaller engines. The big-block engines actually influenced the design of the car which was now adapted to the 5.8 liter unit. Starting with 1973, these cars would be limited because of strict emissions regulations in America. Two high performance versions, the HO and the Cobra Jet were introduced in 1972.
When Ford pulled out of racing in the summer of 1970, there was no longer a need to build a race-specific small-block like the Boss 302. Freed from the cubic-inch limitation of Trans Am, Ford put more cubic inches under the canted-valve 4-barrel Cleveland heads to create the 1971 Boss 351, a SportsRoof-only muscle car that is arguably the best of the legendary Boss Mustangs.
