Franklin O-425
# 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
