The APR CD100016 downpipes replace the 4-cat factory setup with a pair of metal matrix catalysts. In testing, a full APR exhaust produces gains of 25hp and 35lb-ft across most of the engine powerband. Throttle response is also greatly improved. With TIG welding, fully stainless mandrel bent construction, and CNC'ed hangers, you will not find a higher quality system on the market.