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Discussion Starter #2

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Very interesting! :) I'm planning to keep my valve open all the time. Will probably do it by using a dummy to plug the connector into.
 

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Discussion Starter #4
I will be updating this post soon. I am still learning a few things about the performance exhaust and sport exhaust. Like, the exhaust valve is not unique to the U21 option and I will also give more info on the ‘sound generator’.
 

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I will be updating this post soon. I am still learning a few things about the performance exhaust and sport exhaust. Like, the exhaust valve is not unique to the U21 option and I will also give more info on the ‘sound generator’.
Yes, I also wonder how we get this nice sound when the valve button is turned on. The harder we go on the throttle the nicer the sound. It should be the bypass trough the valve section creating this magnificent sound.
 

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Discussion Starter #6 (Edited)
Here's what I've learned so far:
  • The exhaust system components for all AMG's in the same model year are identical. For example, a 2016 CLA45 amg without the U21 Performance exhaust is identical to a 2016 CLA45 amg with the U21 option. The only physical difference between the two cars is the sound generator which is connected to the air intake system and pumps out 'sounds' into the passenger cabin.
  • The sound generator is mechanical in nature but there is a sound generator valve located right next to the generator which opens and closes to allow sounds into the passenger cabin.
  • The sound generator, hosing and valve are located between the engine and firewall so it would be very difficult to add the U21 option to a car without it. Also, the car would need to be reprogrammed to use the sound generator and would also probably need a new wiring harness
  • The exhaust valve near the end of the tail pipe is found on all CLA/GLA amg vehicles. This information come from Mercedes original service and build manuals. It would be nice if the owners here could verify this for me. The valve is easy to see if you look through your tailpipe on the passenger side.
  • The exhaust valve is made up of essentially three parts: the valve inside the tailpipe, a metal part that looks like a coil spring, and an electric motor. The metal 'coil spring' is not really a spring because it doesn't hold the valve open or closed, it just connects the motor to the valve.
  • Removing the 'coil spring' will allow the valve to move freely but there should be enough friction to hold it in place (I have not tested this yet). I will look into a solution to be able to hold it open mechanically. The vehicle will not see any problems or get error codes because the motor is still functioning normally. The motor is just not opening or closing the valve.
  • If you disconnect the exhaust valve electric connector and run the vehicle without this connection, the valve will stay open assuming you disconnected the connector while the valve was open. It's unlikely you will get an error code on your dash but the vehicle may notice that the valve is disconnected and think it's jammed and therefore reduce power.
  • The opening and closing of the valve can be controlled via a switch. Opening the switch (and the circuit) will definitely open the valve but may not necessarily close the valve. I don't think the vehicle will detect anything wrong with the valve but I'm not sure and I need to do some more investigating.
I plan to supply photos, physical and electrical diagrams and more details in the near future. PLease let me know if you have any questions and let me know if you have a valve in your passenger tailpipe.
Jim
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From where do you think the sound enters the cabin? If I put my back seats down, the sound inside is almost twice as loud as with the seats up.
 

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Discussion Starter #8
65569
65570

From where do you think the sound enters the cabin? If I put my back seats down, the sound inside is almost twice as loud as with the seats up.
The sound from the sound generator enters the cabin underneath the dash between the passenger and the driver. The tube from the sound generator going into the cabin is about 40mm (1.5") in diameter.

The increase in sound you hear when you put your back seats down is the sound of the exhaust (mostly the muffler) coming through the trunk space into the cabin. It should be similar to opening your rear windows and hearing the increased exhaust sounds from the muffler/exhaust.

65572

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  • The opening and closing of the valve can be controlled via a switch. Opening the switch (and the circuit) will definitely open the valve but may not necessarily close the valve. I don't think the vehicle will detect anything wrong with the valve but I'm not sure and I need to do some more investigating.
I have also noticed this on my car, however I am running a custom exhaust on my car. I can definitely hear it when I click the button but sometimes when I click the button, I don't notice it, or it takes a while (probably after exhaust fumes are pumped out more gently) to close the valve to prevent problems (?)

Overall, great findings, highly appreciate all the research - never really thought people would be interested in this exhaust enough to write up a whole post about it.
 

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Discussion Starter #15
I finally finished my switches to toggle my exhaust valve and 'U21" valve on and off. I took the ashtray out and mounted the toggle switches there. It's a pretty easy job, just time consuming. I didn't get a chance to the test the U21 valve but I definitely heard a noticeable difference in the exhaust valve especially at 1k to 3k rpms. I put the car in manual mode, sport+ and cruise control at about 3k rpm. I have an audio recording of me opening and closing the valve. If you listen to the recording with ear buds, you probably won't even hear a difference. You need to listen on a system with decent bass. And that is exactly how I would describe the difference in sound - it's not really louder but it is like you turning the exhaust 'bass' from low to high if that makes sense. Anyway, it sounds a lot better.
sound file is on youtube:
65607
 
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