I got defected for noise and i had a 3" turbo back system (with cat) rated at 98db. To get me down to 90dB (the limit), the exhaust place put in a hotdog resonator and silencer for the cannon. I'd say for the 4.5", u might need another muffler squeezed in. As for the sound test, I had trouble finding places in Brisbane who could do it (cos ppl had their machines being repaired) but if u need to come all the way to Brisbane, Valley Exhausts near RBH do the dB test for $55.