Hiro Type 91

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This article is about the engine. For the Hiro Type 91 flying boat, see Hiro H4H.
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 inspired by the Lorraine-Dietrich 12Eb Courlis. 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.