By 1961, Lycoming produced 600 to 700 engines per month. Their most successful post-war products were a series of air-cooled flat-4 and flat-6 general aviation engines. Most famous among these are the O-235 and O-360 four-cylinder engines, and the O-540 six-cylinder engine. Many light aircraft are powered by versions of these engines, with power ratings in the range. Engines in this series also include the O-320 four-, O-580 six- and O-720 eight-cylinder engines, and the advanced turbocharged and fuel-injected TIGO-541 variant of the venerable (carbureted) O-540.