The Franklin O-175 (company designation 4AC-176) was an American air-cooled aircraft engine of the 1940s. The engine was of horizontally-opposed four-cylinder and displaced 175 cu in (2.9 L). The power output was nominally 80 hp (60 kW). A later variant was designated O-180, despite sharing the same displacement.

A related four-cylinder engine of slightly smaller capacity was known as the O-170 or 4AC-171. It produced 60 hp (45 kW).

Variants

O-170

4AC-171

60 hp (45 kW)

O-175

4AC-176

4AC-176-B - 65 hp (48 kW) at 2,200 rpm

4AC-176-BA/(O-175-1) - 65 hp (48 kW) at 2,300 rpm

4AC-176-C - 75 hp (56 kW) at 2,500 rpm

4AC-176-D - 80 hp (60 kW) at 2,650 rpm

4AC-176-F - 80 hp (60 kW) at 2,500 rpm

4ACG-176

O-180

4AC-176-F3 (O-180-1)

Applications

• Aeronca L-3D
• Bowyer BW-1 flying wing
• CAP-4 Paulistinha
• Harris Little Jewel
• Interstate Cadet
• IPT-7 Junior
• Jensen Sport (O-170)
• Johnson-Funke monoplane
• Langley Twin
• Piper J-3 Cub
• Piper J-4
• Piper L-4
• Porterfield Collegiate
• Taylorcraft BF-60 (O-170)
• Taylorcraft BF-65

Specifications (4AC-176-BA2, O-175-1)

Data from Wilkinson^[1]

General characteristics

• Type: 4-cylinder air-cooled horizontally opposed aircraft piston engine
• Bore: 4 in (102 mm)
• Stroke: 3.5 in (89 mm)
• Displacement: 176 cu in (2.88 L)
• Length: 28.6 in (726 mm)
• Width: 30.2 in (767 mm)
• Height: 20 in (508 mm)
• Dry weight: 182 lb (82.6 kg)

Components

• Valvetrain: OHV, 1x inlet valve, 1x exhaust valve operated by pushrods
• Fuel system: 1x Marvel-Schebler MA-3P updraught carburetor
• Fuel type: 73 octane gasoline
• Oil system: Pressure system at 40 psi (3 bar), wet sump
• Cooling system: Air-cooled

Performance

• Power output: 65 hp (48.5 kW) at 2,300 rpm for take-off
• Specific power: 0.37 hp/(cu in) (16.837 kW/L)
• Compression ratio: 6:1
• Specific fuel consumption: 0.49 lb/(hp h) (0.298 kg/(kW h), 220 US gal/(hp h)) cruising
• Oil consumption: 0.003 lb/(hp h) (0.0018 kg/(kW h), 1.4 US gal/(hp h)) cruising
• Power-to-weight ratio: 0.357 hp/lb (0.587 kW/kg)