Harley-Davidson Evolution Engine - Evolution On The Sportster

Evolution On The Sportster

The quasi-unit construction of the Harley-Davidson Sportster, which has been part and parcel with the highly successful model line since its inception, was retained with the Evolution engine upgrade in 1986, resulting in a unique valve train configuration. Unlike almost any other engine in production today, the Sportster Evolution uses one cam per engine overhead valve, resulting in four individual, single-lobe, gear-driven camshafts. The cam lobes are thus all located one behind another, and pushrods are arrayed in parallel fashion as a result. This allows each lifter and pushrod to deflect from the cam lobes perpendicular to the lobe plane. This configuration is friendly to radical, high-output cams, making the Sportster Evolution a natural choice for the once Harley Davidson owned line of Buell Motorcycle Company sportbikes from 1986 up to 2003.

The Sportster Evolution engine has remained largely unchanged from 1986 to 2006, though changes to the transmission, final drive and motor mounts have necessitated changes to the Sportster Evolution case. Construction is almost entirely the same between 883 cc and 1,200 cc versions; the chief difference between the two is a much smaller bore on the 883 cc, along with slightly different heads. Conversions from 883 cc to 1,200 cc are relatively inexpensive and commonplace, and cheaper than the price premium to go from a 883 to 1,200 engine on a new bike. Carburetors were standard on Sportster engines until 2007, when they were replaced by the Delphi Electronic Sequential-Port Fuel Injection (ESPFI) system.