I've scrolled through this forum looking to see what does and doesn't pass emissions a million times and been skeptical about modding my 2015 RT because of fear of failing emissions. But I decided to just go for it and see what happens so here's what I've done and still passed. Comp Cam 270, Kooks Long Tube Headers w/catted mid pipes. Those 2 were my biggest worry but they still passed. I have plenty of smaller mods as well that don't have much of an impact like a Borla ATAK cat back, K&N CAI, ported 87mm throttle body, small stuff like that. Note that I live in Massachusetts so my state probably has different testing than others. Mass does not do the sniffer or the gas cap test. They only plug into the OBD2 and check to make sure everything is running correctly. However, technically they can fail me because my cats are moved because of the long tubes and also my car is very very loud which would also fail me in mass. But as far as the emissions aspect I passed all day long. For the other stuff you just gotta know a guy who knows a guy.