Evolution of the TPF351-20 engine grew from aircraft market demands while enhancing reliability and maintainability through use of proven Garrett engine components and derivatives. The market demanded a high-speed aircraft with passenger comfort approaching that of large commercial aircraft. This required that Garrett develop an engine having a high thermodynamic rating and excellent specific fuel consumption (SFC). In addition, the passenger comfort requirement resulted in a pusher configuration with the propeller plane aft of the passenger compartment and the capability of reduced cruise rpm.Garrett selected an engine design, in response to these requirements, having a high thermodynamic rating (2103 shaft horsepower (SHP) at sea-level static) with a free power turbine driving a rear-drive inline gearbox (1500 SHP flat rated). Due to schedule and reliability requirements, proven components and derivatives from other successful Garrett engines were used to the maximum extent possible. This paper describes how the derivative engine concept was used to provide a free power turbine pusher-configuration engine that was selected for the Embraer CBA123 aircraft.