Thanks Damo, my 550 is at 160,000km. Still runs well, but I think the middle muffler is starting to clog up. From my reading the dump pipe construction is the most difficult. The after market systems separate the Cat from the Dump pipe which maybe a good idea. I also see Dump clearance is difficult. It needs good clearance because of the heat. Good to hear the 3 inch system improves performance. I checked the legal requirements in Victoria, which are very broad. Basically less then 20% power gain, maintain all the original sensors and Cat and its legal.