The third-generation Mustang was produced from 1979 to 1993. Built on Ford’s ubiquitous Fox platform, it evolved through a number of sub-models, trim levels, and drivetrain combinations during its production life.
For 1987, the Mustang received E7TE heads and valve-clearanced pistons. The E7 cylinder heads were sourced from the truck line after the 1986 swirl-port design demonstrated performance problems. Power ratings jumped to 225 hp and 300 ft·lbf (410 N·m) of torque. No major changes were seen in 1988, although the T-roof option for hatchbacks was discontinued midyear. In 1989, the Mustang's speed density air system was replaced with a mass air system. This change slightly reduced factory horsepower, but it made Mustangs much easier to modify. With the mass air system, changes made to the intake, engine, and exhaust system would be recognized and compensated for by the ECU, resulting in a correct air/fuel ratio and optimum power.
Source: Wikipedia, 2012