To get the full benefit of a
TBE you should get a tune/flash ($1000/1500) but if you want and increase in power/torque, have boxer rumble and don't want fork out money for a tune then just go cat back, otherwise it'll run rich using extra fuel because the
ecu is trying to compensate for the extra air flow from a
TBE.
TBE will make more power but not as much without a tune.