The 993 is considered to be the pinnacle of Porsche's vaunted 911 — the last of the air-cooled flat-six, lightweight, and with many of the problems of past 911s sorted out. If there was an ultimate version of the 993 to own, this might be it — a prototype 993 Turbo. Porsche had the bad habit of completely destroying prototypes once they had served their purpose, but miraculously, this one survived. Pulled from the assembly line, the car was sent to Porsche's development department and fitted with its then top-secret engine and transmission. After testing was finished, the engine and gearbox were removed before the car was sold to its current owner After the official introduction of the 911 Turbo to the public, the engine was returned to the owner. Finished in black over a red interior, the car's fascinating history makes it a valuable piece of Porsche history.