"Loud pipes save lives"
That was a kind of yelling cry from Harley riders from the past. The life-saving idea was nice, but 'open exhausts' were mainly things that at least gave the suggestion of power and speed. For breathing the engine it is important that as much fresh mixture as possible can go in and that the exhaust gases can go out as quickly as possible. And with a lot of calculations, everything can be determined between the ideal intake path length at the nominal speed and the coordinated lengths of the exhaust bends, the cone and the spring and diameter of the exhaust silencer.
In the time of many more classic classics there was quite a bit of profit to be gained on the exhaust side. The nozzle occupation had to be adjusted for it, but still.
Perfection ex factory
When the Honda CB 750 and the Kawa 900 came on the market, the "open exhaust thinking" hit again. The four-in-one open outlets could not be carried. And when Das Motorrad tested a whole bunch of them, there was one system that was as much as 14 hp…. less then supplied the original exhaust set. So that was the time when the Japanese engineers showed that they were completely aware of the trick: the full power with an acceptable sound.
Meanwhile, current tests in foreign magazines show that on standard motorcycles little or nothing can be gained in power when mounting a different exhaust system.
A lot of noise
A recent attempt to hang a set of long megatone dampers under an 1991 750 cc Trident was not a success for another reason. Once, under a Trident T150, they sounded beautiful. That T150 turned around an 6.000 rpm. The Hinckley Trident could be canceled up to 10.000 + rpm. And then a couple of Megatons sound like chainsaws that fill a frozen seal. Because you are on your motorcycle you do not hear the exhaust sound itself if you are faster than - say - 80 km / hr driving .. And open riders can feel blessed with that. You only realize what you are doing to the world once you have caught the Westerscheldetunnel on such a free-breathing machine.
Incidentally, the muffled sound of a 'low-revving' twin is subjectively perceived as much less irritating than the whimper of a four-pound running at top speed. And the fact that small children nowadays hide their mother's designer clothes with their hands on their ears when brand new BMW or Honda comes along? That is the result of a parenting simplicity that has been going on for several generations.
It is a consideration and can be an eye opener: Make sure you get behind your own motorcycle. Watch and listen. And enjoy.