I have no problems at all with my test pipe. No smell, no headaches. I have a JDM ITR in a 93 delsol. Although this is only a weekend car/racer. I have no header at this time, test-pipe, 2.5 all the way back to a 2.25 inlet suppertrap.
I have neted 7hp with this set up.
Unless your engine runs on hydrogen, you're going to have an odor, period.