Took some scope pics inside the M muffler.

[onfireX5]

M button off shows the valve closed...on = open. Smooth pipe beyond the valve. No perforations to close up for more sound. Flow design is killer. No baffles to hurt hp.

[Ryngo]

Someone wants to see inside that thing real bad!

[onfireX5]

The primary pipes are perforated and are probably encased like the 70 X5M below. The valved pipes look like they are solid pipe. Owners were modding the 70X5M muffler by welding in a solid section of pipe.

[onfireX5]

Makes sense that the F85 M has a solid pipe based on BMW's exhaust description:

"The exhaust sound of the F85/F86 is geared towards the E7x M, but is much more pronounced. The exhaust flaps are closed when the vehicle is stationary, in the lower engine revs range through all the vehicle speed ranges and when engine dynamics control is set to “Efficient”.
In the upper engine revs range they open in response to the load requirement.
When engine dynamics control is set to “Sport” and “Sport+” the exhaust flaps are stationary and fully open in the lower gears.
In the upper gears the exhaust flaps are closed in the critical ranges, likewise in the upper engine revs ranges in response to the load requirement."

[onfireX5]

Looks like BMW did this to the F85 M :

[onfireX5]

To make this slightly louder.