1991 Harley-Davidson Fat Boy Technical Analysis & Specification Breakdown
At the heart of the 1991 Harley-Davidson Fat Boy custom - cruiser motorcycle, Harley-Davidson utilizes a 1337 cc (81.6 cu in) air-cooled v2, four-stroke layout. In factory specification, peak output is rated at 67 HP (48.9 kW) at 5,000 rpm while maximum torque reaches 97 Nm (71.5 lb-ft) at 2,350 rpm, transferring power to the rear wheel through a 5-speed gearbox and belt final drive. With a specific output of 50.1 HP per liter and a 2,650 rpm working window between peak torque (2,350 rpm) and peak power (5,000 rpm), the engine character is prioritizing low-RPM tractability, mechanical longevity and relaxed throttle response over peak redline numbers.
On the scales, the Fat Boy measures 298 kg (657 lbs) wet (curb), translating to a power-to-weight ratio of 0.22 HP/kg (4.45 kg per horsepower). The 16-liter (4.2 US gal) fuel tank supports practical everyday commuting and weekend road stints, while factory top speed is listed at 148 km/h (92 mph).
Within MotoLibrary's Harley-Davidson archive, this model family spans 7 indexed model years from 1990 to 2026, allowing buyers to track year-over-year changes in emissions tuning, weight and equipment.
Specific Output
50.1 HP/L
Power-to-Weight
0.22 HP/kg (4.45 kg/HP)
Power Band Window
2,350–5,000 rpm
Engine
Displacement1337.0 ccm (81.58 cubic inches)
Engine TypeV2, four-stroke
Engine DetailsV2, four-stroke
Power67.0 HP (48.9 kW)) @ 5000 RPM
Torque97.0 Nm (9.9 kgf-m or 71.5 ft.lbs) @ 2350 RPM
Use this page to compare this motorcycle by its real specifications, not only by model name. Focus on the details that affect fit, comfort, handling, range and ownership.
Power
Compare engine output with similar motorcycles if acceleration, highway use or two-up riding matters.
Torque
Torque is useful for judging real-world pull, especially for touring, commuting and loaded riding.
Fuel Capacity
Fuel capacity helps estimate touring range and how often you may need to stop.
Brakes
Brake setup is worth comparing if you ride in traffic, mountains or with a passenger.
Suspension
Suspension details can matter for comfort, road feel and long-distance riding.
Transmission
Transmission and final drive affect maintenance, smoothness and everyday usability.
