The Evolution Engine of Harley Davidson
The Evolution Engine, commonly known as Evo, is a 45-degree V-twin engine created by Harley Davidson, primarily for its Big V-twin motorcycles. This engine was introduced in 1984 and replaced the Shovelhead engine until 2000.
The Evo engine was developed for Harley Davidson's Big V-twin bikes, with a 1340cc displacement. It replaced the Shovelhead engine and was later succeeded by the Twin Cam 88 engine in 1999 for the Touring and Dyna models. The engine was also used in Sportster models with 883cc and 1200cc displacements. The 1100cc version was available until 1988.
Harley Davidson was nearing bankruptcy when the Evolution Engine came to the rescue. The Evo engine was a crucial factor in the company's revival following its buyout by AMF in 1981. The name change was likely part of a strategy to reshape the company's image.
Sportster
The Evo engine used aluminum for its cylinder heads, rocker boxes, and cylinders, making it lighter than the previous cast-iron designs. Aluminum also offered better thermal conductivity, which improved the air cooling effect. This innovation played a key role in the engine's success.
The Sportster Evolution engine design differs significantly from the Big Twin. The Sportster uses a single camshaft per engine with overhead valves, leading to four individual gear-driven camshafts. The cam lobes are positioned behind each other, with pushrods placed parallel to the cylinders in pairs.
Other Bikes
The Evolution engine was used in limited edition CVO FXR4, FXR2, and FXR3 models until 2000. Before that, it powered the FXR, Touring frames, Softail, and Dyna models for 15 years. The final limited edition saw changes to the top-end, but the case was only slightly modified compared to the Shovelhead engine.
In the Big Twin engine, the vertical plane of the cylinder rockets becomes perpendicular to the cam lobes. The camshaft is located above the crankshaft axis, with the 1340cc Evolution engine using a single four-lobe camshaft.
