Want to upgrade the exhaust on my Slant ...size matters?

If I was gonna do that, I would run 3inch into a 3"-in muffler, and whatever, out,lol. Why? Cuz the cost of the pipe upsize is minimal, and that cannon will present nearly atmospheric pressure to the 2bbl. Any backpressure in the system and the 2bbl will probably show little to no improvement. I can say that Cuz I know. I think I had more power with the big 1bbl.
Of course 3" is overkill, so what. The installed cost is nearly the same. Ok at least 2.5.......