i had a konig rear section, on when i did the test pipe, so i cant say for sure but it would have to make it louder, even with stock muff. only prob i had with test pipe was a hella stinch, when pulling to a stop the gas fumes would come back around the pass. side and about gag you, hince the word test pipe, i couldn't stand it on the street daily, but it did make a lot of difference than stock cat.