[jdean]

Along with air filter and any other accessories, you would be surprised how much power is lost through the side pipes. The efficiency of Cobra type side pipes varies a great deal, and can cost up to 30-40 horses. A lot of times when an engine that has been dyno'd with headers only is put in the car and then taken to a chassis dyno, this muffler restricted loss is lumped in as drive train loss.