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Allison V-3420


The Allison V-3420 was a large experimental W-configuration 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 liquid cooled V-3420 was essentially a pair of 12-cylinder Allison V-1710 in 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.

V-3420-A16R (-11)

V-3420-A16L (-13)
left hand rotation of propeller, 1-stage supercharger with 1-stage turbo-charger and intercoler

V-3420-A18R (-17)

Supercharger ratio 7.2:1

V-3420-B (-23)
Similar to the -A but with mechanically driven supercharger in two variable speed stages.


V-3420-A18R (-17)
Type: 24-cylinder turbosupercharged double-"Vee" liquid-cooled piston engine
Bore: 5.5 in (139.7 mm)
Stroke: 6 in (152.4 mm)
Displacement: 3,420 in3 (56 L)
Length: 97.7 in (2,482 mm)
Width: 60.0 in (1,421 mm)
Height: 38.7 in (863 mm)
Dry weight: 2,655 lb (1,204 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 turbocharger with intercooler
Fuel system: Bendix-Stromberg PR-58B3 three-barrel injection-type downdraught with automatic mixture control.
Fuel type: 100/130 Octane
Oil system: Pressure fed at 60-70 psi (4.2 - 4.9 kg/m²)
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 46.0 inHg / +8.0Lb boost for 15 minutes
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
Max. Cruising
1,575 hp (1,175 kW) at 2,300 rpm at 25,000 ft (7,625 m)
Specific power: 0.76 hp/cu in (34.6 kW/l)
Compression ratio: 6.65:1
Specific fuel consumption: 0.41 lb/hp/hr (11 g/kW/hr)
Oil consumption: 0.025 lb/hp/hr (138g/kW/hr)
Power-to-weight ratio: 1.0 hp/lb (1.64 kW/kg)



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