K really wanting to know wtf is going on with the pipes on those bikes. On the first one has he actually rebuilt the entire exhaust system? I've been thinking of a mod for this bike but was more keen on routing it down to one pipe and off to the side rather than up to four. Also would like to see what each of them did with the rest of the exhaust system, specifically the catalytic converter section.

Personally, I'd be more interested in performance and fuel economy than the noise, but wow, the tone of that second bike is quite pleasing.