Not to a legal standard whilst maintaining the flow of a straight 3.5" exhaust, decent CAT and acceptable ride height etc etc - on a skyline.
People including myself have been there and tried, you come close, but just not enough.
Another car with a different floor pan, then possible if you could get mufflers on there that are larger again... But 2-3dB is actually a substantial amount of noise to soften.
It's the noise of the motor and the 4700/5100 RPM that the tests are done at that sets the meter off. They also measure "back off" noise too, which often a crack/pop will set the meter off over the limit.
3" you can get passed however, as i said in post #4