I would be willing to bet the tube diameters are close, but where the big difference would be found are in the 4-2 junction and the 2-1 junction. The SR unit is nice and smooth. The joints are tapered inside and out. I'm not sure the Stock 4-2-1 is that good.
Leave it to Random to Needlessly complicate things.
Leave it to Random to Needlessly complicate things.