My buddy drives a new 6.7L cummins with the epa crap gone and tuned. Just had to go through emissions with it and passed with flying colors. That makes me really want to know why they slap all that emissions crap on, when he could easily get it to pass without it. And his mileage has increased big time without it which in turn
Not all of the EPA crap works to the good. Much of it is to reduce the NOx emissions. Inherently, diesels have very low CO2 and HC emissions. Their primary emissions that are to be controlled are NOx and particulates. Particulates are the visible portion that shows up as smoke. NOx are oxides of nitrogen that are formed at high combustion temperatures. Passing an emissions test is not an indication of low NOx emissions. NOx tests have to be done under load, and require some very expensive and sophisticated equipment. As such, removing "EPA crap" usually results only in increased NOx emissions, and will pass aftermarket emission tests.