Similarities

• The Lycoming IO-360 and IO-390 engines are four-cylinder air-cooled reciprocating engines with fuel injection. The cylinders are horizontally opposed just like the old air-cooled Volkswagen Beetle engines. They both have the same short block. The differences are in the engine displacement and other equipment added to the short block.
  
  

The IO-360

• The IO-360 has an engine displacement of 360 cubic inches. This series comes with either a 180 horsepower (hp) or a 210 horsepower output. The higher horsepower is the result of a higher compression ratio. The 180 hp has an 8.5 to 1 compression ratio; the 210 hp has an 8.7 to 1 compression ratio.
  
  

The IO-390

• The IO-390 uses the same short block as the IO-360. The cylinders are bored out to bring the engine displacement up to 390 cubic inches. Lycoming made this engine to meet the demand of kit aircraft builders who wanted more horsepower than the IO-360 without the higher compression ratio.