I had no intentions of using the stock exhaust at all, i had pre-bought a bunch of 3" piping, resonator, muffler and 3" v band flanges. I bolted up all the hot pipes, drove with an open downpipe for a few days then finished up the rest of the exhaust. I ended up side exiting it to save work & wieght.
I did not have a supercharger. Straight from NA to turbocharged. I never gained any strange codes nor running problems. Coolant temps, intake temps all good. AFRs stayed 14.5 ish to 1 at all cruising speeds, and high 13s at WOT. With methanol injection, small nozzle, WOT is 12.5:1.