after market ECUs, turbos, bigger injectors and blah blah blah are all ILLEGAL as they can/will change emissions from the factory settings.
sure some people might get lucky and pass with these mods every now and then, but it dont mean they are legal.
there is however an emissions test (i think) you can have done for a few grand and if pass it you are able to run the above said mods, but dont take my word for it...