title: Franklin O-425
text: # Franklin O-425
  
  The Franklin O-425 (company designation 6AG/6V6) was an American air-cooled aircraft engine that first ran in the mid-1940s. The engine was of six-cylinder, horizontally-opposed layout and displaced 425 cu in (7 L). The power output was between 240 hp (179 kW) and 285 hp (213 kW) depending on variant. The O-405-13 (6V6-300-D16FT) of 1955 was a vertically mounted, turbocharged and fan cooled version for helicopters.
  
  ## Variants
  
  ### 6AG6-245
  
      Geared propeller drive at 0.623:1, 245 hp (183 kW) at 3,300 rpm, (XO-425-5).
  
  ### 6AGS6-245
  
      Supercharged and geared, 250 hp (186 kW) at 3,200 rpm, (XO-425-3).
  
  ### 6V6-245-B16F
  
      Vertically mounted, fan-cooled helicopter version, 245 hp (183 kW) at 3,275 rpm, (XO-425-1).
  
  ### 6V6-300-D16FT
  
      Vertically mounted, turbocharged, fan-cooled helicopter version, 285 hp (213 kW) at 3,275 rpm, (O-425-13).
  
  ## Applications
  
  * Convair XL-13
  * Republic YOA-15 (intended)
  * Sikorsky S-52
  * Sikorsky YH-18
  * Stinson L-13
  
  ## Specifications (O-425-5)
  
  Data from Aircraft engines of the World 1950.
  
  ### General characteristics
  
  * Type: 6-cylinder air-cooled horizontally-opposed aircraft piston engine
  * Bore: 4.75 in (120.7 mm)
  * Stroke: 4 in (101.6 mm)
  * Displacement: 425.3 cu in (6.97 L)
  * Length: 47 in (120 cm)
  * Width: 33.3 in (84.6 cm)
  * Height: 30 in (76 cm)
  * Dry weight: 405 lb (184 kg)
  
  ### Components
  
  * Valvetrain: 1 x exhaust and inlet OHV driven by pushrods and rockers
  * Fuel system: 1 x Bendix-Stromberg PS-780 up-draught carburetor with automatic mixture control
  * Fuel type: 80 Octane / US Army 2-103 all-purpose motor fuel
  * Oil system: Pressure system at 55 psi (380 kPa)
  * Cooling system: Air-cooled
  
  ### Performance
  
  * Power output:
  
     * Take-off: 245 hp (183 kW) at 3,300 rpm
  
     * Normal: 240 hp (180 kW) at 3,200 rpm at sea level
  
     * Cruise: 168 hp (125 kW) at 2,840 rpm at sea level
  * Specific power: 0.58 hp/cu in (26 kW/L)
  * Compression ratio: 7.4:1
  * Specific fuel consumption: 0.51 lb/hp/h (0.086 kg/kW/ks)
  * Oil consumption: 0.015 lb/hp/h (0.0025 kg/kW/ks)
  * Power-to-weight ratio: 0.606 hp/lb (0.996 kW/kg)
  * Reduction gear: Planetary reduction gearing at 0.623:1
  