TOPIC:

What a great discussion! Here's a brain dump of what I think I know. Forgive me if I go on a bit.

From what I know about dual exhaust systems on V8-equipped cars, any system design that allows gases to escape from any given cylinder through as many mufflers as possible will yield both better performance and lower sound levels. In other words, for a typical V8 installation, after the headers but before the mufflers, you would have a crossover pipe between the two sides. It seems that the exact size, length, and curvature matter less than the mere fact of having a cross-over in the first place.

The most "elegant" design IMHO is a pair of 45 degree bends, where the outside of the bend on both sides is cut off, and the two welded together so that gasses on either side have a straight shot through to the opposite side, but still maintain a path to their "own" muffler. I heard a system like this on an Olds 4-4-2 at the dragstrip years ago. The exhaust note from that 455 was the weirdest thing I've ever heard--lots of people actually ran over to see what it was. To me, it sounded like I imagined a large-displacement V12 would sound. Like there were more power pulses than any V8 could produce.in a given time. There are also X-pipes that use a pair of stamped sheet-metal pieces to join the four pipes, almost exactly what your fabricator has made for you. The brand "Pypes" has these type for your education.

I also have a '77 GoldWing (a flat four) that originally came with a very sophisticated exhaust system called the "horse collar" by enthusiasts. It had a very large common plenum between the two sides, and a couple of "stinger" outlets that I assume had some kind of glass-packed silencers in them. It is renowned for being quiet enough for the touring set, while still allowing superbike performance. Honda really couldn't decide which market they were trying for, which is what makes these 1st-gen bikes so fascinating for me. In the case of my GW, the original system was long gone, except for the headers. I just attached a pair of factory Harley Sportster mufflers after that. These used to be a dime a dozen in like-new condition ten years ago, because the first thing any Harley Boy wants to do is make it louder, so there were thousands of take-offs to be had on eBay, dirt cheap. I think I paid $40 for mine, including shipping.

If I had your bike, and the access to a talented fabricator like you seem to have, the next thing I would try would be adding a fairly large crossover tube between the two plenums. Like maybe 2" in diameter, even flattened to an oval for clearance, or whatever size you can fit. I would do that and evaluate the sound before anything else.

If I was to go radical with my '82 13, I would keep the original collectors and outlets, but add a crossover tube right after them, before the mufflers. If I kept the OEM "baffle boxes" or whatever you call them, I don't think I would even need mufflers, per-se. As it is, I replaced the huge "cannon" mufflers with a pair of Chinese glass-packs about 1/3 the external size, but the same core diameter. The sound is aggressive, but at 60 MPH the sound of the wind over my helmet is still louder than the exhaust. My GW is a bit louder, which may be because I Installed the mufflers using 22 degree bends to create an upswept-muffler design.

To give the six-into-six look you have, I would have gone with essentially a dual exhaust with 1-into-3 tips.

Yep, that cross over pipe is also beneficial for cylinder scavenging, it creates a wider power band. I have one on the custom exhaust on my Z1300, it's a 2" pipe running between the two rearward flowing pipes. Whether it's actually beneficial on a six cylinder engine is debatable though, because our bikes didn't have one originally (I don't think the CBX had one either?). They certainly are beneficial on a crossplane crank V8, I know that, be it an "H" or "X" pipe. As you say though, it also serves as supplemental silencing, as then the exhaust noise pulses are shared by both sides of the exhaust system, doubling it's silencing capabilities. Which is why they were used by manufacturers so much on bikes with the original systems.

Well, I got all the required items through the post today and set about creating the mufflers with what I had.

Here pics on how I did it and a video link at the end to see/hear the result. I did not have to drill any holes as the fit was very tight and I had to hammer the tubes down to the right level. They ain't gonna come out by themselves I think, but I'll check over the next few miles..

























I'm pretty chuffed with the result. Idle and low revs it now sounds deep and powerful, but not as 'cackingly' loud as before, and at speed its nice and loud. There is also no performance loss I'm happy to report (or none that I can notice, still running in and keeping it below 4000 revs).

So I'l leave it like this for now and see how I go.

Cheers all

Paul

Nicely done. They look very professional. I'll be curious to see if the packing rides up the baffles because of the lack of inner cone (the other half of the dog bone.) But if the coppers pull you over for noise, you've got baffles in their face.

Glad it worked out, looks & sounds well I reckon the Acousafil will expand to make them an even tighter fit