So far I have installed a simota cold air intake, B&M short shifter, and Mazdaspeed axleback muffler, and dealer installed window tint. I also replaced the stereo with an Alpine head unit and added a subwoofer, and replaced the factory speakers with Pioneer. I will be installing a header when I can afford it (talk my wife into it). It's my understanding that there is not much that we can do to the 2.0 engine to increase hp without replacing the internals. I am open to suggestions if you have any.