Bandit exhaust internals

I have a 1200N that has a tuned motor from a previous owner (since deceased), the downpipes appear to be stainless steel and look stock but with a modified one off end-can. The exhaust rotted through just after collector box and it appeared to have been cut open at sometime and a mild steel section welded in, I gave the exhaust to a mate who cut out the mild steel section & replaced with stainless, when he returned the exhaust he said that there appeared to be an arrangement of pipes within the exhaust that appear to turn the gases back on themselves and then back again down a narrower pipe.

Does anyone know whether this is standard or added later possibly to increase back pressure ?

Since this was removed the bike is very hesitant to pick-up gradually between 3000-4000 rpm but if I bang the throttle open is barely noticeble, but of course my missus does not appreciate this riding style!!!!

The standard can and link pipe are a waste of space, I junked mine and got a beowulf can that came with a new link pipe, saves weight and looks a lot nicer, and the bike goes better too which is what you want...