title: Franklin O-400
text: # Franklin O-400
  
  The Franklin O-400 (company designation 8AC) was an American air-cooled aircraft engine of the 1940s. The engine was of eight-cylinder, horizontally-opposed layout and displaced 397 cu in (6.5 L). The power output was 235 hp (175 kW).
  
  ## Variants
  
  ### 8AC-398
  
      200 hp (149 kW) at 2,600 rpm.
  
  ### 8ACG-398
  
      235 hp (175 kW) at 3,500 rpm. The 8ACG-398 was unusual in using a reduction gearing for take-off and direct drive for cruising.
  
  ## Specifications (8ACG-398)
  
  ### General characteristics
  
  * Type: 8-cylinder air-cooled horizontally opposed aircraft piston engine
  * Bore: 4.25 in (108.0 mm)
  * Stroke: 3.5 in (88.9 mm)
  * Displacement: 397.2 cu in (6,509 cc)
  
  ### Components
  
  * Valvetrain: OHV
  * Cooling system: Air-cooled
  
  ### Performance
  
  * Power output: 235 hp (175.2 kW) at 2,600 rpm
  