Removing restriction from your exhaust system is the key to added performance. Increasing piping size effectively does this, but with the stock catalytic converter in place you are still loosing horsepower. Invidia eliminated this with their catless test pipe. The test pipes are 60 or 70mm and are constructed of stainless steel. These pieces will finish off your exhaust system nicely and free up every last bit of power from your motor. You can also opt for their test pipe with CEL fix which will disable the check engine light you will get from running this pipe.
Honda S2000 2000-2009