Excluding actual DB measurements, the exhaust should sound 'similar' to the original factory fitment. Other than that a loud exhaust could just make you a target for the law.... to be fair some owners do abuse the noise to the max.
"the exhaust should sound 'similar' to the original factory fitment..." Mmmmm, that would be 0DB then
My intention was never to abuse the law, just wanted to be different... approaching my 40's ( ), i'm not your typical "boy-racer" any more - hence I drive a Lexus