I've had my car for 2 years now, and now that I've decided I'm going to keep it for a long time I thought it would be nice if I did a little upgrading. . What’s the best exhaust for 6.7 power-stroke for performance and fuel economy? I loved this but I'm not sure about the choice. I am wanting to slowly do the exhaust, then cold air intake and then a chip of some kind. Are they all the same besides what they are made of? I am only getting around 13 MPG so I am wanting to try to get that up some. Is straight piped or a muffler better or is it personal preference? Thanks.