title: Bristol Neptune
text: # Bristol Neptune
  
  The Bristol Neptune was a seven-cylinder air-cooled radial engine developed in 1930. It had the same size cylinders as the earlier Mercury and Titan engines, 5.75 in (146 mm) x 6.5 in (165 mm) which gave a displacement of 1,182 cu in (19.3 L) and produced a maximum of 320 horsepower (239 kW). The Neptune was effectively a seven-cylinder version of the Titan.
  
  ## Applications
  
  * Bristol Type 110
  
  ## Specifications (Neptune I)
  
  Data from Lumsden.
  
  ### General characteristics
  
  * Type: 7-cylinder air-cooled radial engine.
  * Bore: 5.75 in (146 mm)
  * Stroke: 6.5 in (165 mm)
  * Displacement: 1,182 cu in (19.3 L)
  * Diameter: 48.4 in (1229.3 mm)
  * Dry weight: 630 lb (286 kg)
  * Designer: Roy Fedden
  
  ### Components
  
  * Valvetrain: Overhead valve, Four valves per cylinder
  * Fuel type: 73-77 octane petrol
  * Cooling system: Air-cooled
  * Reduction gear: Direct drive, left hand tractor
  
  ### Performance
  
  * Power output: 295 hp (220 kW) at 1,700 rpm (rated power), 320 hp (239 kW) at 1,870 rpm at sea level
  * Compression ratio: 5:1
  * Power-to-weight ratio: 0.5 hp/lb (0.83 kW/kg)
  