Harley-Davidson Evolution engine

This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these messages) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Harley-Davidson Evolution engine" – news · newspapers · books · scholar · JSTOR (December 2009) (Learn how and when to remove this message) This article possibly contains original research. Please improve it by verifying the claims made and adding inline citations. Statements consisting only of original research should be removed. (December 2009) (Learn how and when to remove this message) (Learn how and when to remove this message)

The Evolution engine (popularly known as Evo and sometimes as Blockhead ) is an air-cooled, 45-degree, V-twin engine manufactured from 1984 by Harley-Davidson for the company's motorcycles. It was made in the 1,340 cc (82 cu in) displacement for Harley-Davidson Big V-twins bikes, replacing the Shovelhead engine until 2000 when the last EVO was placed in a production factory custom FXR4 (FXR2 and FXR3 were the first CVOs). In 1999, it was replaced by the Harley-Davidson Twin Cam 88 in the Touring and Dyna model and in 2000 in the Softail models. Also available in the Sportster model beginning in 1986, it was made in the 1,100 cc (67 cu in) displacement until 1988 and is still made in the 883 cc (53.9 cu in) and 1,200 cc (73 cu in) ^[1] displacements for the Harley-Davidson Sportster, replacing the ironhead Sportster engine.

Most analysts consider the Evolution to be the engine that saved the reorganized Harley-Davidson company from certain bankruptcy. Harley-Davidson's official name for the engine was likely related to the company's attempt to reform its image following the 1981 management buyout from previous owner American Machine and Foundry (AMF).^[2]

Both the heads and cylinders of the Evolution engine are made from aluminum to reduce weight compared to a cast iron design. Air cooling efficiency is improved as aluminum is a superior thermal conductor to cast iron. The blocky rocker boxes (thus becoming nicknamed "block head" which never caught on), aluminum heads and cylinders (also referred to as "jugs") are the only part of the Evolution engine that can be said to be essential; the Big Twin and Sportster incarnations of the Evolution are significantly different.