The 1981 Harley-Davidson Shovelhead engine is an air-cooled 45-degree V-twin engine that powered the majority of 1981 model year Harley-Davidson motorcycles. The 1981 Shovelhead engines displaced 1340 cubic centimeters and produced 67 horsepower using an overhead valve system with two valves per cylinder. Shovelhead engines were about 10 percent more powerful than the older "Knucklehead" engine designs used on earlier Harley-Davidson motorcycles.
All of the "Big Twin" Harley-Davidson motorcycles produced during 1981 used the Shovelhead engine, also known as the Shovelhead 80, due to its displacement of 80 cubic inches. However, Sportster models used a smaller Sportster-specific V-twin engine that only displaced 1 liter. The 1981 Shovelhead engine was almost always mated to a four-speed manual transmission, except in the case of the 1981 Tour Glide and Tour Glide Classic that used a transmission with five speeds.
While the basic design of the Shovelhead engine dates back to 1966 and Harley-Davidson had standardized the engine's size in 1978, the 1981 version of the Shovelhead did have some significant differences from earlier models. A new V-Fire II electronic ignition made starting up the Shovelhead easier, and the engine also had additional drainage and longer valve guides. The compression ratio of the 1981 engine was also reduced to 7.4:1.