The downpipe is a critical part of the exhaust system in a Subaru. From the factory, it is very restrictive due to the catalytic converters and the smaller diameter piping. The Invidia downpipe changes that and will increase power and torque significantly, especially when professional tuning is done. Stainless steel, 3 inch piping will hold up for a long time and flow a lot more exhaust than stock. This downpipe also features an extra bung for an O2 sensor if you wish to use a monitoring device or gauge for your AFRs. Lastly, this particular version has a high flow catalytic converter built in for emissions friendly use. This is a bolt on piece that includes hardware. If you are using a stock catback exhaust, you will need an adapter to fit it properly.