To experience the full performance of the 125cc Aprilia engine, catalytic converters needs to be deattached from the engines exhaust Pipe. This means that the original manifold of the SX 125 must be replaced. If no catalytic converter is used, the pipe is completely continuous, so the sound of the exhaust changes as well. Of course to experience even the full sound of the Aprilia SX 125 the decibel-eater needs to be removed from the Arrow muffler
Either this or that, the certification of the rear silencer is no longer valid.