I was catch one day with 120 DCB on S 13 .You have to provide a noise test must by 92 DCB I think .
So go in to shop and buy steel wool and push in to exhaust / muffler and put silencer but before You put silencer in , wrap a lot of steel wool around silencer . , then push in the muffler.
Was working for me from 120 to 86 DCB.
Any better mufler shop can provided test for You.