Harley-Davidson engines are easy to identify and help categorize the motorcycle. There have been seven major engine revisions in the history of Harley-Davidson.
Flatheads
Flatheads were made between 1929 and 1974. Instead of overhead valves, the valves on flatheads are on the side of the engine and open up to a chamber next to the combustion chamber. Flatheads were desirable for their simplicity. Their displacement is 45 cubic inches (742 cc).
Knucleheads
Knuckleheads were made between 1936 and 1947. They came in 60 cubic inch (990 cc) and 74 cubic inch (1,200 cc). These were overhead-valve V-twins with telltale "knuckly" valve covers that help in identification.
Panheads
Panheads were made between 1948 and 1965. It has pan-like covers where the knuckles used to be. It also has aluminum heads and internal oil lines. It came in 60 cubic inch (990 cc) and 74 cubic inch (1,200 cc).
Shovelheads
Shovelheads were made between 1966 and 1985. Its distinctive head looks like a shovel. Its displacement is 74 cubic inches (1,200 cc).
Evo
The Evolution engines made between 1984 and 1999 displaced 81.8 cubic inches (1,340 cc). However, current Sportster models use Evo engines with 883 cc and 1,200 cc displacements. The Evo was a radical redesign that included electric start and square blocks over the valves.
Twin Cam 88
The Twin Cam 88 started manufacture in 1999. It got its name from the dual cams in the crankcase. It is the largest Harley engine now in production, displacing 88 cubic inches (1,450 cc). In 2007 it became known as the Twin Cam 96.
Revolution
The Revolution engine started production in 2001 and is used on only one model--the VRSC. The engine is water-cooled--unlike the earlier models, which are all air-cooled; the V angle is 60 degrees instead of 45. It has four overhead cams and electronic fuel injection. It is smaller than the Twin Cam--69 cubic inches (1,130 cc)--but it can rev to 9,000 rpms and has 115 horsepower.
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