The Continental O-520 is a six-cylinder, horizontally-opposed aircraft engine, first run in 1963 as a development of the O-346. It has been produced in versions incorporating fuel injection (IO-520), turbo-charging (TSIO-520), and gearing (GTSIO-520).
The IO-520 series of engines normally produced 285-310 HP and were used in numerous aircraft such as certain models of the Bellanca Viking 300 and Super Viking, the Beech Bonanza and Baron, and the Cessna 185, 206, 210, 310 and 400 series of aircraft. It has largely been superseded by Continental's newer IO-550 engine. The IO-520 series of engine is considered to be a reliable engine, but some of the early versions of this engine had a weaker crankcase than subsequent versions. Versions featuring more substantial crankcases are often referred to as having "heavy crankcases."
The GTSIO-520 was not as common and in its most common application (the Cessna 404 and Cessna 421 twin-engine aircraft) it produces 375 horsepower (280 kW). Gearing reduces the RPM of the propeller making the engine quieter running than many other engines.