S&S SB100 ebgine...1640cc (100ci) 4" bore 4" stroke. Their ratings are a little high, S&S has a dyno sheet on that engine and it's more like 111-115hp...which starts to become not so impressive for a $9000 crate motor that you still need to spend another $1000 or better to get a transmission and primary set up. You can get the engine for 1986-2003 solid mount sporties or 1996-2002 tubeframed buells. But still the bikes are beautiful!! I especially like the Racer variation and supposedly they have a supercharged version that makes 210hp...