For enthusiasts looking for the highest possible exhaust flow from their vehicles, removing the factory catalytic converters in favor of 2.5" diameter race or "test" pipes is the most efficient upgrade available. The 370Z/G37/350Z Test Pipes replace the factory catalytic converters and are designed purely for off-road performance. By getting rid of the dense OEM catalytic converter cores exhaust flows freely from the engine, increasing peak power output.