Hi BG305. Unfortunately I was not monitoring my emission before or after the tune. If you have the Fabspeed tune, they may have deactivated parts of the emission monitoring to prevent the MIL light activating.
Hi Peter. I think you could install the stock mufflers on the Fab speed cat headers, but it would surprise me if it improve your torque / horsepower at lower RPM. Attached are my dyno runs, comparing the stock car to maxflow to supercup. I did not test the configuration you were talking about which is the new headers with the stock muffler. Nevertheless you can see from the charts that in all runs the Fab speed results were better than stock across the entire rev band.
