What to use for loud exhaust?

My apologies. I missed that.
That said, I'm wondering just what exactly your exhaust guy had in mind in the design. Merge collectors are meant to capture the pulses and assist in evacuating the other pipes being collected to draw a negative pressure increasing performance. In order to do that, the collector needs to be larger in volume than the header pipes but not too large. otherwise the effect is lost. Then in your case, the tailpipes are attached to the opposite end of the collection Box but are directly opposite the header pipes. So I'm suggesting that the pulses will be sort of balanced out but a majority of the individual pulses will carry on through the collector box and out each individual pipe. I'm thinking that if you held your hands over the left or right 3 pipes, at idle you would feel the individual pulses 3,2,1-3,2,1 or 4,5,6-,4,5,6 almost as if the pipes were through pipes.
I have a brand new DG pipe in a box waiting to go on my beast BUT when I saw this pic

I knew I was going to have to build those pipes. Love the look and appreciate the design. 6 in to 2 in to 4. As far as exhaust design, the only more effective design would have been 6 in to 2 in to 1 I really wanted to spoof my KZ to appear to be a CBX but with a water cooled engine? Head turner. Then seeing this exhaust new I was going to have to build it.
Anyway, I digress. Looking forward to seeing your resolve here and I do appreciate your end goals as far as appearance. Quite unique. Kudos.
KB

Ah, so it's a 6 into 2 into 6

Yes, that is why I was expecting him to put some/a baffle(s) in the 2 boxes, so as to make the gasses 'go round' the obstacles and so lose some of the sound there.... but he said he didn't put anything in, so I think you are right, everything goes straight thru.

As the pipes are 'glued' in to the boxes, I wonder how difficult it would be for him to still insert a baffle in there ...? I'll have to ask.

But it does make me wonder that if I put dog bones in the tail pipes, will the gasses and pulses still carry straight thru? How will noise get reduce with wadding around the side where no gasses go thru? (or do I need to read the book!?)

Quote: You could try packing with mineral wool (as an example Rock wool insulation batting material. I can tell you that insulating a room with fibreglass pink and insulating a room with rock wool, the room with the rock wool is silent compared to the same size room with the fibreglass pink. The rock wool is also fire proof to 1900 F. Unquote .... Rockwool, is that the stuff you put in the roof for heat insulation? I have a full roll of that still lying around... I might try that too.

And yes, I have seen that design a while back. I just wish Kawasaki would actually build it!

.... maybe that is and idea for the next build - take an old z1300 and build it to emulate that one... !!

Paul

Paul, a straight through perforated tube with packing around it is exactly what's inside all bike race cans & car performance mufflers. They muffle some of the sound (as well as giving a deeper pitch) at lower revs but hardly at all at higher revs. So what you're planning to do will work. It's exactly the construction of the stubby cans on mine.

That computer rendering above of the Z1300 was done by a fella called Kar Lee, he would do a modern make over for a different classic bike every month on a page titled "Retro Re-boot" in Classic Motorcycle Mechanics magazine here in the UK. They asked for suggestions on what bikes to do next so I Emailed him to ask if he'd do the Z1300 which he eventually did. Not saying it was completely down to me as there were probably multiple suggestions for the Z1300 lol.

I'll thank you for poking him to do it. It's awesome !! I just wish it was an overbore 4 valve per cylinder.