Story
The 1968 Ford Mustang GT 390 represents Ford's highly successful translation of big-block power into its iconic pony car chassis. Contemporary and reference sources consistently identify the model around a combination of the heavy-duty "S-code" 390-cubic-inch FE V8 engine and the factory-optional GT Equipment Group package, rather than as a separate coachbuilt or independent tuner edition. Built entirely on Ford's factory assembly lines in Dearborn, San Jose, and Metuchen, the GT 390 was a factory-built, mass-produced performance vehicle designed to counter the rising threat of GM's big-block Chevrolet Camaro and Pontiac Firebird.
The core of the GT 390's identity is its S-code powertrain. Sourced records and period technical specifications document an OHV 390-cubic-inch FE V8 featuring a 4.05-inch bore and 3.78-inch stroke, a 10.5:1 compression ratio, and a single Holley four-barrel carburetor. This setup carried factory gross ratings of 325 horsepower at 4,800 rpm and 427 lb-ft of torque at 3,200 rpm. Power was routed through either a heavy-duty, close- or wide-ratio Toploader four-speed manual transmission or the C6 SelectShift Cruise-O-Matic three-speed automatic, transmitting output to a robust Ford 9-inch rear axle.
Chassis and suspension upgrades were integral to the GT package. In 1968, the GT Equipment Group required the heavy-duty handling suspension, which featured stiffer front and rear springs, heavy-duty shock absorbers, and a thick front stabilizer bar. Power front disc brakes, which were optional on lesser Mustangs, were standard equipment on GT-package cars. Visually, the package was defined by grille-mounted fog lamps, GT-styled steel wheels with unique hubcaps, dual exhaust exiting through quad chrome tips under the rear valance, and distinctive GT side striping.
Authenticity cautions matter here. The cultural significance of the 1968 Mustang GT 390 is heavily tied to Steve McQueen's Highland Green fastback in the film Bullitt, which has led to a high volume of replica and tribute cars. Badge, paint, and general styling are weak evidence by themselves. Stronger proof requires manufacturer documentation such as a Marti Report, window sticker, or the S engine code in the vehicle identification number and corresponding door data plate. Specific axle ratios and assembly plants are left out until stronger documentation is attached.