What's the deal with the exhaust valves on BMW's S58-powered cars?
- 3 min reading time
BMW's S58-powered cars are equipped with new and improved exhaust flap actuators, which can move in between open and closed positions. Along with this comes a specific ECU calibration which affects the exhaust note and volume outside the car. The common fix for this issue is to install a valve controller, which enables drivers to fully open and close the valves at all times.
BMW's renowned 3.0L inline 6, dubbed the "S58", has been making waves in the automotive industry. However, enthusiasts who have stock cars may be hit with a wave of disappointment when they try to make some noise. There is a lot of talk about the S58, especially when it comes to their exhaust valves. But what exactly sets them apart from the traditional valves we all know and love? Let's delve into the details of this innovative technology.
What makes the exhaust valves in BMW's S58-powered cars unique?
Unlike traditional exhaust valves that are either fully open or fully closed, the exhaust valves in BMW's S58-powered cars come with a new type of exhaust valve actuator. This actuator allows the valves to be moved to a variable position in between fully open and closed. This was likely implemented to meet new, even stricter noise regulations, but also for comfort by reducing unwanted noise in the cabin.
How do the different maps or tables in the ECU affect the exhaust valves?
Within the engine control unit (ECU) of BMW's S58-powered cars, there are different maps or tables that determine how much the exhaust valves will open. These maps are carefully calibrated to ensure that the valves open to the optimal position based on various factors such as engine speed, load, and drive mode .
For example, here is the base exhaust flap map for an 8AT S58:
This table shows the relationship between gear (0 being neutral, 9 being reverse), engine speed, and exhaust valve percentage (from 0—fully closed to 100—fully open). Many would be surprised to see that the exhaust flaps do actually open up all the way! If you look towards the bottom left corner, you will see that the flaps are completely closed in 5th, 6th, 7th, and 8th gear at low RPMs, presumably to eliminate any drone in the cabin. The S58s are known to be on the raspy and droney side, especially compared to the B58s.
However, this table is not all that goes into the final exhaust flap opening percentage:
Here, we can see values between 0 and 1. The values here are multiplied with the values from the "Exhaust flap base position" table above. This table shows the relationship between throttle pedal torque request (in Nm) and engine speed. Again, presumably to reduce unwanted noise, in a good portion of the low to mid torque area the valves are completely closed.
The keen-eyed among you may have also noticed that the table above was for Sport+ (engine) mode. In Comfort, it looks a lot different—only opening when it absolutely has to (for engine performance reasons).
In combination, these two tables cause the exhaust flap to modulate while driving, and may create a weird sound outside the cabin, especially if you have any exhaust modifications. To solve this issue, we recommend looking into purchasing an exhaust valve controller (dual valve), which enables you to force the valve fully open or closed. A single valve variant is also available for M Performance and base models.
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