Ok, so after installing the Power Kit I figured I need some sound too
I ordered and installed the BMW Performance Exhaust.
In the cabin, if the windows are closed the change in sound is very subtle. No droning, nothing to bother you. The exhaust note is not very deep (in the cabin).
Outside, the sound is very nice and seems very "engineered". Its different from classic aftermarket exhausts. Its not very loud, but it always attracts attention because of the way it sounds, not because of the loudness.
When cruising, the exhaust is barely noticeable at all. Its just like stock, with just a little hint of "something" coming from the rear mufflers. No drone at all.
When accelerating to higher RPMs, the sound is more powerful but I don't really feel that it has made the engine note prettier. The nicer engine note is from 2000 to 4000RPM. After this it feels just like before but louder (from inside the cabin).
If you are in an underground parking, the sound is just incredible !
I didn't expect changes in power, that's why I had some reticence when purchasing the exhaust. But surprisingly, I felt the engine really does breathe better, you just feel there is less restriction. I felt a power increase from midrange (2500RPM) to top, but I don't know if it is real or not. But what I am sure of is that the engine seems significantly less restricted.
So, is it worth the money ? I would say no. Since you are inside the cabin most of the time, the sound improvement is not very significant. Before getting this, definitely get the Power Kit.
Also, if you want a perfectly balanced exhaust, this is it. No drone, Not very loud, but it always atttracts attention because the way it sounds.
Here are a couple of videos shot in an underground parking:
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