Most of the Buell street bikes utilize the air-cooled 1203cc Thunderstorm V-Twin. It powers the XB12R Firebolt, a partially faired street bike, as well as the XB12S Lightnings – naked street bike designs. The adventure-touring Ulysses also uses the Thunderstorm Twin, with the new 1125CR sourcing the 1125 Helicon V-Twin.
History of Buell Motorcycles 