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 90 600 hp water-cooled W-12 had also been developed, producing 600 hp.

Applications

• Aichi E10A
• Aichi E11A
• Hiro H4H
• Kawanishi E7K
• Mitsubishi Ka-9

Specifications (Type 91 500hp-1)

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

Components

• Cooling system: Liquid-cooled

Performance

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