Currently in Euro 4 exhausts, not sure if in the F6, is a restriction ring, from what I understand it's there to aid the cat in heating up quicker than previous models as the cat is very close to the turbo, yet at operating temp it's effectively a 2.5" system from the start. I've gone ahead and had this ring removed today with a die grinder as it's only held in with 3 small welds. This is located on the outlet from the cat section of pipe at the flange. I was concerned that it may throw up a