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Allison V-3420 Engine
Type Liquid-cooled X-24 piston engine
Manufacturer Allison Engine Company
First run 1937
Major applications P-75 Eagle

The Allison V-3420 was a large experimental American piston aircraft engine, designed in 1937.



In 1937, at the behest of the United States Army Air Corps, the Allison Engine Company agreed to design and build a large-displacement high power aircraft engine. The resulting V-3420 was essentially a pair of 12 cylinder Allison V-1710 engines mated to a common crankcase with a 30° angle between the inner cylinder banks. The crankshafts of the two V-1710 engines were geared together to drive a common propeller shaft. Most V-3420 parts were interchangeable with those for V-1710-E and -F engines.

The V-3420 had a power-to-weight ratio of 1.6 kW/kg or 1 hp/lb, excellent for its time. It was envisioned as a powerful yet compact engine for several advanced Air Force projects of the day, including the Douglas XB-19, the Boeing XB-39 Superfortress, the Lockheed XP-58 Chain Lightning, and the General Motors P-75 Eagle. As none of these designs reached full-scale production, only about 150 V-3420s were built.

Specifications (V-3420)


General characteristics

  • Type: 24-cylinder turbosupercharged double-"Vee" liquid-cooled piston engine
  • Bore: 5.5 in (139.7 mm)
  • Stroke: 6 in (152.4 mm)
  • Displacement: 3,421.2 in³ (56.06 L)
  • Length: 100.0 in (2,540 mm)
  • Width: 56.0 in (1,422 mm)
  • Height: 34.0 in (864 mm)
  • Dry weight: 2,600 lb (1,180 kg)


  • Valvetrain: Single overhead camshaft per 6-cylinder block, two intake and two exhaust valves per cylinder, sodium-cooled exhaust valves.
  • Supercharger: Single-speed one-stage gear-driven supercharger
  • Turbocharger: General Electric
  • Fuel system: Bendix-Stromberg PT-12E1 three-barrel injection-type downdraft with automatic mixture control.
  • Cooling system: Liquid-cooled with a mixture of 70% water and 30% ethylene glycol, pressurized.


  • Power output:
    • 2,600 hp (1,940 kW) at 3,000 rpm at 25,000 ft (7,625 m) for 15 minutes
    • 2,100 hp (1,565 kW) at 2,600 rpm at 25,000 ft (7,625 m) maximum continuous power
  • Specific power: 0.76 hp/in³ (34.6 kW/L)
  • Compression ratio: 6.65:1
  • Power-to-weight ratio: 1.0 hp/lb (1.64 kW/kg)

See also

Related development

Related lists


  • Bridgman, L, (ed.) (1998) Jane's fighting aircraft of World War II. Crescent. ISBN 978-0-517-67964-7

External links


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