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Exhaust - Description of Loud / Quiet and 'Always Loud' Mod


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@Paul_D great sum up, great pictures, big thanks 👍  If this topic existed before, we wouldn't mess up 3 other topics 😁


@BrendonianPeople usually use aquarium valve 4/6mm to bung the pipes. Screw was suggested as well. I also read something about the hot glue 😃



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  • Gold FFM

A small bolt is one simple thing to use, which is what I had previously.

I've now got a slight variation on the above set-ups where I can now have the exhaust valve forced into quiet mode regardless of rpm, just in case I ever fail a static noise test even with my add on silencer. This would only be for a few seconds whilst the noise test is done. I wouldn't run the car on track with the valve closed, but at least I'd be able to get on track and see how I fare with the drive-by readings. 

Valve 1 is normally kept shut. Valve 2 is normally open. The car works exactly as per normal, and I use the dash switch to make the car loud if I want.

However if I needed it to be forced closed, I can close Valve 2, open Valve 1 and vacuum is permanently applied. The car is forced into quiet mode.



Exhaust Vacuum Paul.jpg

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  • 2 months later...
On 29/10/2021 at 20:35, Paul_D said:

There's been a few topics where people have talked about the exhausts on the car, and how to make it permanently loud via various methods. 

Although people may know to pull pipes and block things off, they may not always fully understand what they're achieving. I thought it might be worth a quick explanation for people to use as a reference in the future.

The exhaust is made quiet or loud by closing or opening a butterfly valve in the exhaust. When the valve is open, it lets the exhaust gasses through a much bigger pipe. The valve is moved by an actuator, which uses a spring and diaphragm. The spring pushes the valve open, and a vacuum pressure is applied to pull it back the other way and close the exhaust valve. 

The vacuum is generated by the engine, and goes to a vacuum reservoir. The outlet of this goes to a solenoid valve. The solenoid valve switches so the outlet is either at vacuum or atmospheric pressure. The cars ECU controls the solenoid valve. 

All this is much easier to understand in pictures. (Don't laugh at my dodgy Microsoft Paint diagram please) 

In 'Loud' mode the solenoid valve has removed the vacuum pressure from the red hose going to the actuator AND vented it to atmosphere so the the pressure isn't trapped.

In 'Quiet' Mode, the vacuum path goes all the way through to the actuator.

Once you understand that, the mod to remove / bung the vacuum pipe becomes more clear. The outlet (red) pipe is removed (or cut as in the third diagram). This instantly puts the actuator at atmospheric pressure so the exhaust moves to the 'loud' position. It's worth putting a bung in the removed pipe to stop dust getting in. You also need to put a bung on the outlet of the solenoid valve, as otherwise you've got a vacuum leak and the system will be sucking in dirt and stuff. That's why cutting the pipe is potentially easier than removing it, as you can quickly bung both pipes in the same way.

In the final diagram where the pipes are cut, this is where some people install a small aquarium valve instead. You then open or close that little valve to block the vacuum to the actuator or not.  

Hopefully this might be of some use to people in the future. 

Exhaust Vacuum Loud Mode.jpg

Exhaust Vacuum Quiet Mode.jpg

Exhaust Vacuum Bunged.jpg

great write up and diagrams @Paul_D

So what happens when you upgrade to a third party full exhaust system. Would these principles still apply?

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In theory it should be the same, as long as the 3rd party exhaust is valved in the same way and simply connects to the existing vacuum pipe and remains controlled by the standard ECU.

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The real fun starts when you simply keep valve 2 in place electronically, but disconnect the vacuum and have it run through a separate valve you then switch from the cabin.  Like I did.  So you can have the car always loud or always quiet with the flick of a switch.  Mind you, don't do this with the OEM back box, esp. not the +380 one (due to the very small pipe diameter for the "quiet" trajectory => lots of back pressure).  



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