Here is an interesting solution suggested by the Porsche Club due to really stringent noise levels at Lime Rock last year.
This is my 360 Challenge with advanced noise suppression acquired in the canned goods aisle of a local deli. I did this after I got black flagged for noise. Amazingly, it worked perfectly. Only later did we discover that heat buildup melted one of my
oil cooler lines.
Anyway, sold that car and am now the proud owner of a Superformance Daytona coupe which has real and very loud side pipes. No way will they pass at some of the tracks. I tried the Vortex cone mufflers, but they only quieted things down a little (I just shoved them up the tailpipe and tack welded them). I too need some real sound reduction, but don't want to lose too much hp in back pressure. The Brillo pads seem like a good short term solution, but what kind of hose do you use so it won't melt? And how about back pressure?
If anyone finds a simple easy slip-in solution (my side pipes have turnouts, so it needs to be something flexible), please post it here.