I came from a domestic quad, so I was confused when people talked about the Big 3, too. It's a performance kit that EHS sells. A full exhaust, air intake lid (for more efficient air intake), and a fuel programmer (to add fuel so the engine doesn't run lean with all the new air). I think most people consider any bike with aftermarket intake, exhaust, and programmer a Big 3 bike, whether it's EHS components or not. But I could sure be wrong about that.