Replace or upgrade the downpipe in the exhaust system of your 2004.5-2005 Chevy/GMC 6.6L LLY Duramax. Upgrading to an aftermarket downpipe with larger diameter tubing and smooth mandrel bends can offer increases in horsepower and torque and help lower exhaust gas temperatures (EGT's). The factory OE downpipe typically incorporates unnecessary bends or crimps in the tubing restricting exhaust flow. You can find all the top brands including AFE, AP Emissions Technologies, Banks Power, BD-Power, Dorman, Fleece, PPE, Magnaflow, MBRP, and more!