In this video I test the noise difference between having the exhaust valve closed vs 10%, 25%, 50% and 100% open. Can we adjust exhaust sound level with a adjustable exhaust valve controller?
Is there any difference in noise between different openings? And if so, how much is the difference? And is it worth fitting a variable exhaust valve controller to be able to open the exhaust valve variable amounts?
Test Results
| % Open | Normal Drive Away | Slow Drive-By | Medium Launch | Normal Drive-By |
| 0 | 69 | 76 | 75 | 84 |
| 10 | 85 | 82 | 87 | 84 |
| 25 | 88 | 83 | 87 | 87 |
| 50 | 85 | 86 | 88 | 87 |
| 100 | 86 | 84 | 88 | 87 |
Adjustable Exhaust Valve – Test Result Analysis
The first thing that strikes me is there is a clear difference with the exhaust valve being completely closed. The second thing that I notice is there is not much difference between the exhaust valve being 10% open and 100% open. Sure it is quieter at 10% open but the difference is not night and day. The biggest difference in exhaust volume is between the exhaust valve being fully closed and 10% open.
Launch Numbers
I did two types of “launch”. The first was pulling away from a standstill normally, like I would driving normally. The other was a 50% aggression launch from a standstill.
As I said above, the difference between 10% open and 100% open was not as big as I expected. For the medium launch, the small difference may be down to not getting into the throttle 100% until I was around 100 meters from the sound meter. The further away from the meter the closer the sound volumes became. Having said that the volume differences for the normal drive away were also low.
Conclusion
Although the difference in volumes was not as great as I was expecting, there was still a difference. If you want a small amount of exhaust volume adjustability, an exhaust valve controller that can open the exhaust valve a variable amount has some merit. If you just want to have a quiet exhaust and a loud exhaust, using the vacuum valve that these valved exhausts are supplied with will do the job. How you control that either valve is up to.
From what I see, these valved mufflers are supplied with a remote which you manually turn on or off. If you want an automated system I think you need to make something yourself.
The exhaust valve in this video used an electric servo. The vacuum valve need to be connected to a vacuum reservoir if the valve needs to opened under full throttle and especially on turbo engines. The mufflers are supplied with the required valves (and pumps if you don’t want to use an engine vacuum source).