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  The Harley-Davidson "panhead" engine is a vintage motorcycle engine that the iconic American motor company utilized in many of its motorcycle models manufactured from 1948 to 1965, when the engine was retired for an updated model. Though Harley offered a number of different trim levels for each of its bikes that used the panhead engines, there were only three main panhead versions: a 61-cubic-inch model, an early 74-cubic-inch model that offered slightly more power, and a later 74-cubic-inch with dramatically more power.
  
  

Panhead E and EL Engines

• The Panhead E and EL engines had displacement of 61 cubic inches and generated 8.77 horsepower. Bore and stroke of the E and EL panhead engine were 3.3 inches by 3.5 inches. The only differences between the E and the EL are the compression ratios, which are reported at 6.5 to 1 for the E and 7 to 1 for the EL engine.
  
  

Panhead F and FL Engines

• All F and FL engines were 74 cubic inches and had bore and stroke of 3.4 inches by 3.9 inches. Generating 9.44 horsepower, this panhead engine's compression ratio also deviated slightly between the two models. The F's compression ratio was 6.6 to 1 while the FL model's ratio was 7 to 1.
  
  

Panhead FLH Engine

• The FLH-model panhead engine was available to riders from the 1955 model year through 1964. Like its FL predecessor, it was 74 cubic inches and had a 3.4-inch bore and 3.9-inch stroke. Compression ratio was higher, reported at 8 to 1. The engine produced significantly more power: 60 horsepower at 5,500 rpm and 65 pound-feet of torque.