a secondary throttle. The TC model is certified for flight to , with an advertised turbo critical altitude of , giving a maximum true airspeed of . PA-24-300 In 1967, one aircraft was modified with a Lycoming engine for trials. It did not enter production. PA-24-380 Two prototype aircraft were built in 1961. They were standard Comanche airframes, but had Lycoming IO-720-A1A engines with a three-bladed propeller. The design was modified with an even larger engine and produced as the PA-24-400. Comanche 400 The PA-24-400 Comanche 400 was produced from 1964 to 1966. Only 148 PA-24-400s were built. The Comanche 400 is powered by the , horizontally opposed, eight-cylinder Lycoming IO-720 engine, developed specifically for the model. Cooling problems have happened with the rear cylinders. The Comanche 400 has a three-bladed propeller and carries of fuel, or with optional extended tanks. Fuel burn was advertised as , at 55-75% power. The high fuel burn means that it is expensive to operate. The 400 had a typical empty weight of and a maximum gross weight of . Book speeds for the PA-24-400 included a cruising speed of and a top speed of . While identical in planform to other PA-24 models, the 400 is structurally strengthened, primarily in the tail, with an extra nose rib in the stabilator and the vertical fin. The stabilator, vertical fin, and rudder of the 400 share virtually no common parts with the 180, 250, or Comanches. Twin Comanche PA-33 In 1967, a single Comanche was modified by Swearingen with a pressurized cabin. The prototype, powered by a Lycoming O-540 engine and equipped with Twin Comanche landing gear, was designated the PA-33. First flown on March 11, 1967, the prototype later crashed on takeoff in May 1967 and the project was cancelled. World records Max Conrad In June 1959, Max Conrad flew a Comanche 250 on a record-breaking distance flight in Fédération Aéronautique Internationale C1-D Class, for aircraft from to less than . Having removed the interior seats and replaced them with fuel tanks, Conrad flew nonstop from Casablanca, Morocco, to Los Angeles, a distance of . When the aircraft took off from Casablanca, it was heavily overloaded and just cleared the airport fence. The Comanche 250 Max Conrad flew for this flight is now located in the museum at the Liberal, Kansas, airport. On November 24–26, 1959, Conrad flew a Comanche 180 on a distance