This paper describes Pratt & Whitney Aircraft's performance improvement program for its JT8D turbofan engines. Retrofit kit programs for existing in-service engines and major new engine programs have evolved from this effort which has been underway since 1978. Changes are being made to the fan, compressor, and turbine sections of the various engine models to improve component efficiency levels and significantly decrease engine thrust specific fuel consumption. Retrofit packages will provide thrust specific fuel consumption reduction of 2.1 percent for JT8D-1 and -7 engines, 3.0 percent for JT8D-9 engines, and 5.5 percent for JT8D-15, -17 and -17R engines at cruise conditions. Fuel savings at other conditions are comparable.