I'm surprised that no one that swapped out their stock active mufflers cut open one. I looked at pictures online and closest I found was a 2018 muffler w/o active exhaust.No ...
This.
It's easy enough to suss out looking up the tail pipes
WD
This is exactly correct. It's a conventional muffler with a perforated straight pipe going from inlet to outlet with the valve at the end. The second tailpipe is connected to the muffler case.The pipe behind the valve comes strait from the mid-muffler.
The pipe without the valve is only indirectly connected to the mid-muffler via the rear muffler.
The pipe in front of the valve is perforated; the gases flow into the rear muffler via the perforation.
The more the valve is closed, the more gas is forced through the rear muffler.
When it comes to sound, it's as @Skye describes an acoustic issue.
If it's all about loud and quiet, you can simply say the more gas that can flow directly out, the louder it exits.
So valve open means straight pipe, but the perforation still has an influence on the sound, without this it would sound different and may also be louder.
This effect is used by companies that offer a different rear silencer, in which the pipe behind the flap is an unperforated pipe, e.g. this exhaust:
She purrs...
Our euro exhausts get delivered like this :
That is the great underbody protection supplied by Ford Europe, which is probably applied at the import harbor.Our euro exhausts get delivered like this :
Very informative. ThanksOur euro exhausts get delivered like this :
Which looks a bit shit if your one of those people that doesn't just look at the wheel, but you are tempted to look past the wheel :
So why it was off I took the opportunity to strip it and have it metallic ceramic coated - it should keep it looking good (especially compared to 'as supplied') and it should keep about 30% of the radiated heat away from the diff without having to wrap that area.
Anyhow, the descriptions on how the box works further up this thread are perfect, but I can add a bit more info when you reference these three photos.
Note the spot welds around the box :
They hold an internal baffle plate. splitting the box into two chambers.
I will call the first smaller chamber number 1 and the second larger chamber number 2.
Chamber 1 has a condensation drain.
Here is the non valve outer exhaust pipe internals :
That's the outer box wall you can see (remember our euros have a GPF so the internals are pretty mush as clean as the day they were made).
That pipe is perforated and runs through both chambers, pretty much up to the outer box wall.
Here is the valve inner / central exhaust pipe internals :
Note it was really hard to get a good photo down there as the valve took all the flash and the focus.
By naked eye, you can see straight down it, out of the back of the box and right to the first bend in the exhaust tubing.
Like the outer pipe it's perforated and as best as my eye can make out, I think the pipe has a small gap in it that vents into chamber 1 i.e. rather than one continuous pipe, it looks like two pipes perfectly in line, but slightly separated.
So ...
Valve open = Gas is straight though both chambers with some pipe perforations.
Valve closed = Gas backs up behind the valve. (depending on the box stuffing in chamber 2) a small proportion of the gas will pass through the perforations into chamber 2 and out of the perforations into the other tailpipe. Majority of the gas will pass through the pipe separation into chamber 1, head to the back of the box, to exit the other tailpipe passing some more perforations on the way.
Hope that helps - and saves @skinnyb from taking the sawzall to his exhaust ... lol
WD
Techline CermaKrome. Its stable up to 815°C and really meant for manifolds so it should easily cope with the heat in the rear section
