Thanks John. Mine has the same issue, lots of us burnt fuel igniting in the exhaust on the over run. I don't mind this popping and banging but as you say it b*ggers the Cat. Mine has a locked Cosworth Map so was hoping that I didn't have to have it re-mapped. I suppose the best thing is to try it and see. This will be the second Raceco exhaust I used and yes they are somewhat quieter than the CC quite ones, as well as being very pleasing to the eye!