PWood - The engine size is 1340CC. The only difference between "Evo" (in non-Sportster applications) and "Big Twin" is that the term "Big Twin" is broader as it covers Panheads, Shovels, Evos, TC88´s, etc. The term "Evo" refers to "Evolution" - the motor that Harley manufactured from 1984 to 1999 in between the "Shovelhead" (1966 to 1983) and the "Twin Cam 88" or "FatHead" (1999 to present). The term "Big Twin" refers to the larger cc (usually 1200cc and larger, non-Sportster) engines that Harley manufacture(s)(d). "Big" = larger and "Twin" = 2 cylinder. An "Evo" is a "Big Twin" (bearing in mind that there were also "Evo" Sportsters (stock 883, 1000 and 1200cc). Ken (Duke)