 Currently, production underbone model with the largest engine displacement is the SYM VF3i, which is powered by a fuel-injected 183 cc SOHC 4-valve water-cooled engine.Historically, underbones led the way in semi-automatic transmissions and indicator systems.In other respects, the technical sophistication of underbones tended to lag those of larger motorcycles, but nowadays they are increasingly equipped with similar electronic ignition, fuel injection etc.