Pratt & Whitney's design changed to incorporate a 15% larger fan, increasing bypass ratio from 0.25 to 0.30.
The ATF's increasing weight required more thrust to meet the performance requirements, and required max thrust increased by 20% to 35,000 lbf (156 kN) class. Pratt & Whitney and General Electric were selected to make prototype engines, designated YF119 and YF120 respectively, for demonstration and validation. The original RFP called for maximum thrust in the 30,000 lbf (133 kN) class. This technology allows the engine to achieve very high core temperatures to meet the requirement for high specific thrust for supercruising. The combustor, designated Floatwall, eliminates welds to mitigate crack growth due to thermal cycling. The fan and compressor stages were to use integrally bladed rotors (IBR) to reduce weight and cost and improve performance. The high pressure and low pressure turbines were single stage and counter-rotating, thus shortening the engine by removing a row of stators and saving weight.
Advances in engine technology, such as those from the Advanced Turbine Engine Gas Generator (ATEGG) and the Joint Technology Demonstration Engine (JTDE) programs, allowed the design to do more work with fewer stages, with the PW5000 having only 6 compressor stages compared to the F100's 10 compressor stages. Detailed design of Pratt & Whitney's submission, designated internally as PW5000, began when the request for proposals (RFP) for JAFE, later renamed ATF Engine, was released in May 1983. The F119 resulted from the Joint Advanced Fighter Engine (JAFE) program in the early 1980s aimed at supplying the powerplant for the Air Force's Advanced Tactical Fighter (ATF).