Silencers

[deltarider]

My silencers look still nice from the outside, but I have no illusion on the inside. When kicked, you can hear it rattle inside, indicating not all interior material is where it is supposed to be. I had the same with my first set which lasted some 75.000 km and thereafter was happily welcomed by an other CB500 owner. I always wondered to what extend this affects the correct 'breathing' of the engine. I know an exhaust must produce some back pressure to have the combustion chambers adequately filled, but... is the form of the first half of the exhaust responsible for this or are the dampeners in the rear part, which silence the sound of more importance? To be on the safe side, I have chosen to run my bike just slightly richer than standard, meaning I've raised the needles one notch. All the rest is standard.

[Sesman]

Length and shape mate….as the actress said to the bishop😳

[SumpMagnet]

the whole 'back pressure' thing is a bit of a fallacy.

The valves control the flow of the exhaust gases, and when your inlet valve is open ( bar the period of overlap ) the exhaust valve is closed.
When the exahust valve is open, you want to get the spent mixture out as quickly as possible...and restricting that with back pressure isn;t a help.

Race exhausts are less restrictive than road pipes and have less back pressure as a result. Noise however, is a factor. Road pipes had to deal with that far more than race pipes.

What is critical, as Sesman said, is length and shape. This controls the harmonic resonances that can help pull spent gases out, and prevent loss of the fresh charge where there is a lot of valve overlap.
In a 2-stroke...this is where expansion chambers get their effectiveness from. Controlling how these shock pulses resonate back is why pipes need to be the right length and shape, ands if you want to ruin an exhaust...cut a chunk out of the middle and weld the ends back. Some one made it the length it was for a reason!

the baffles in the back end are to make the thing less noisy, and to do so without losing too much flow.

I dabbled with home-made exhausts way back, and used to have an excellent book on the subject full of formula's to work out lengths of plain pipes, megaphones etc. Sadly..it's long gone.

[K2-K6]

As already noted, the dimensions cause planned effects in extraction of gasses from combustion chamber. The primary pipes and their change in size as they enter the silencer chamber are timed for higher rpm, with the longer part of pipes working at the lowest rpm.

Internal corrosion, they aren't plated so just a plain steel material vulnerable to conditions. Burnt fuel produces mild sulphuric acid as byproduct from sulphur in original fuel, with obvious results. High use and heat helps to minimise, with cold starts/short journeys particularly bad for internal conditions.

Running richer won't help you in preserving pipes, leaner will. Most vehicle exhaust in current times benefit from more concise fuel metering with nothing like the problems seen years ago for exhaust lifing. This is an obvious concern for bikes on here that have high priced exhaust sets.