Design and development
These engines were commonly vertically mounted and used to power many early helicopters in the United States. They were closely related to the 2A4 and 4A4 2- and 4-cylinder engines. In various subtypes, the 6A4 remained in continuous production from 1945 to the time Franklin's United States operations ceased in 1975, with versions continuing in Polish production into the 1990s.
In 1947 this engine was modified into a water-cooled version by the Tucker Car Corporation for use in the 1948 Tucker Sedan. Tucker liked the engine so much that he purchased the Aircooled Motors/Franklin Engine Company, and it remained under the ownership of the Tucker family until 1961.
O-335-1
Military designation of vertical installation model for helicopters
O-335-3
Similar to -1 but changes in starter installation
6A-335
180 hp (134.2 kW) at 2,800rpm
6AL-335
150 hp (111.9 kW) at 2,600 rpm
6A4-125
125 hp (93.2 kW) at 2,200rpm
6A4-130
130 hp (96.9 kW) at 2,200rpm
6A4-135
135 hp (100.7 kW) at 2,450rpm
6A4-140
140 hp (104.4 kW) at 2,375rpm
6A4-145
145 hp (108.1 kW) at 2,600rpm
6A4-150
150 hp (111.9 kW) at 2,600rpm
6A4-165
165 hp (123.0 kW) at 2,800rpm
6A4-200
200 hp (149.1 kW) at 3,100rpm
6AG-335
220 hp (164.1 kW) at 3,400rpm
6AG4-185
185 hp (138.0 kW) at 3,100rpm
6AGS-335
260 hp (193.9 kW) at 3,400rpm
6AS-335
240 hp (179.0 kW) at 3,200rpm
6V-335-B
210 hp (156.6 kW) at 3,100rpm
6V-335-A1A
200 hp (149.1 kW) at 3,100rpm
6V-335-A1B
200 hp (149.1 kW) at 3,100rpm
6V4-165
165 hp (123.0 kW)
6V4-178
178 hp (132.7 kW) at 3,000rpm
6V4-200
200 hp (149.1 kW) at 3,100rpm
6VS-335
225 hp (167.8 kW) at 3,200rpm
Data from
Type: 6-cylinder air-cooled horizontally opposed direct drive supercharged aircraft piston engine
Bore: 4.5 in (114.3 mm)
Stroke: 3.5 in (88.9 mm)
Displacement: 335 cu in (5.49 l)
Length: 37.4 in (950.0 mm)
Width: 30.8 in (782.3 mm)
Height: 21.6 in (548.6 mm)
Dry weight: 307 lb (139.3 kg)
Valvetrain: OHV, 1x inlet valve, 1x exhaust valve operated by pushrods
Supercharger: mechanically driven supercharger
Fuel system: 1x Marvel-Schebler MA-3SPA updraught carburettor
Fuel type: 80 Octane gasoline
Oil system: 80 S.U. secs (15.6 cSt) grade pressure fed at 40 psi (275,790 Pa), wet sump
Cooling system: Air-cooled
Delco-Remy direct cranking electric starter motor
Power output:
(Take-off): 150 hp (111.9 kW) at 2,600 rpm for take-off
(Normal): 150 hp (111.9 kW) at 2,600 rpm at sea level
(Cruising): 112 hp (83.5 kW) at 2,350 rpm at sea level
Specific power: 0.45 hp/(cu in) (20.35 kW/l)
Compression ratio: 7:1
Specific fuel consumption: 0.51 lb/(hp h) (0.311 kg/(kW h), 229.5 US gal/(hp h)) cruising
Oil consumption: 0.01 lb/(hp h) (0.006 kg/(kW h), 4.5 US gal/(hp h)) cruising
Power-to-weight ratio: 0.488 hp/lb (0.8 kW/kg)
B.m.e.p.: 137 psi (945 kPa)
