Just installed a 40 series original Flow on my 05 Supcrew & used the stock tailpipe. For some reason my factory muffler was 2.5" in & 2.75" out. Tailpipe is 2.75 all the way. Installed a dual out with turndowns on friends 05 Supercab yesterday & his was typical 2.5 all the way. Sorry I'm concerned with the details, what's the story?

 

My truck was 2.5 all the way from the tailpipe to the cats. The muffler shop that put mine on cut off the pipe right after the cats and installed a 3" pipe from then on. He did an awesome job, bent the 3" pipe down to size to slide right onto the 2.5" and then welded it and ground it down to look completely normal.