Craig
I tried last year but it didn't work out too well. I borrowed a decibel meter from a friend and decided to check my side pipes as follows: one with nothing in it and one with the insert in.
I fired up the car and immediately put the meter off the scale, which went up to 128 or 130, on the side with no insert. This was just above idle and back 5 or 10 feet. Unfortunately, I got exactly the same result for the pipe that had the insert. So much for science. I can tell you that the car is much louder without the inserts. I also have shorty pipes that are even louder than the empty long pipes.
Wayne
Wayne