title: Franklin O-405
text: # Franklin O-405
  
  The Franklin O-405 (company designation 6AC-403) was an American air-cooled aircraft engine of the 1940s. The engine was of six-cylinder, horizontally-opposed layout and displaced 405 cu in (6.64 L). The power output was between 200 hp (149 kW) and 250 hp (186 kW) depending on variant. The O-405-9 (6ACV-403) was a vertically mounted, fan cooled version for helicopters.
  
  ## Variants
  
  ### 6AC-403 (XO-405-1)
  
      200 hp (149 kW) at 2,750 rpm
  
  ### 6ACSA-403 (XO-405-3)
  
      Supercharged, 220 hp (164 kW) at 2,750 rpm
  
  ### 6ACGSA-403 (O-405-5)
  
      Supercharged, geared propeller drive at 0.632:1. 250 hp (186 kW) at 3,200 rpm
  
  ### 6ACV-403 (O-405-9)
  
      Vertically mounted, fan-cooled helicopter version, 245 hp (183 kW) at 3,275 rpm
  
  ## Applications
  
  * Culver XPQ-15
  * Doman LZ-1A
  * Doman Pelican
  * Fairchild XUC-86B
  * Fleetwings XBQ-1
  * Kellett XR-8
  * Sikorsky R-6
  
  ## Specifications (6AC-403/XO-405-1)
  
  Data from
  
  ### General characteristics
  
  * Type: 6-cylinder air-cooled horizontally opposed aircraft piston engine
  * Bore: 4.625 in (117.5 mm)
  * Stroke: 4.0 in (101.6 mm)
  * Displacement: 403.2 in³ (6.6 L)
  * Dry weight: 405 lb (184 kg)
  
  ### Components
  
  * Cooling system: Air-cooled
  
  ### Performance
  
  * Power output: 200 hp (149 kW) at 2,750 rpm
  