Hiro Type 91

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Type 91
Type W-12 water-cooled piston engine
National origin Japan
Manufacturer Hiro Naval Arsenal
Developed from 12Eb

The Hiro Type 91, (full designation Hiro Type 91 520 hp water-cooled W-12), was a 12-cylinder, water-cooled, W engine developed for aircraft use by the Imperial Japanese Navy in the mid-1930s. Power was in the 450 kW (600 hp) range. Its design was derived from the Napier Lion. An enlarged more powerful engine, the Hiro Type 90 had also been developed, producing 600 hp.


Specifications (Type 91 500hp-1)[edit]

General characteristics

  • Type: 12-cylinder water-cooled W-block (3 banks of 4 cylinders) aircraft piston engine
  • Bore: 135 mm
  • Stroke: 160 mm
  • Displacement: 27.5 L


  • Cooling system: Liquid-cooled


  • Power output:
  • 620 PS for takeoff
  • 520 hp for max continuous

See also[edit]

Related lists


Gunston, Bill (1986). World Encyclopedia of Aero Engines. Wellingborough: Patrick Stephens. p. 74.