I disagree that increasing scavenging is always good to achieve improved performance.

Scavenging works best at low RPMs when there is the greatest exhaust pulse gap that creates more following vacuum. As RPMs increase the pulse gap decreases and the benefit of scavenging reduces. Scavenging benefit increases if the exhaust pipes are smaller because the smaller pipes increase the exhaust velocity which creates a greater pulse and corresponding vacuum that follows.

The problem is that the smaller the pipe the greater the back pressure. When scavenging is not good is when scavenging increases back pressure. In the case of forced induction such as turbo charging that use the exhaust to function, the pulse is already smoothed out so the pulsing necessary to create the vacuum needed for scavenging benefit is gone.

Drone is caused by resonate frequency. A change in resonance can result in drone. I agree that drone should not be due to the installation of an X pipe but there is that potential. That's why my suggestion is to do something that someone else has done with no drone outcome. FYI-I thought an X pipe made the exhaust louder. My only reference were Youtube videos that sounded louder to me but could easily been where the microphone was placed. I agree, it would be far less likely to create a drone if the result of an X pipe is a quieter and smoother sounding exhaust.

I think, if you can achieve the sound you want by lowering back pressure it is always a better route.

In our cases, yours because of the supercharger and mine because of nitrous, we have too much back pressure even with the Dinan exhaust. I have decided electric cutouts are my best investment. It will result in a greater performance gain due to decrease in back pressure. I won't get the 20% increase that could come from headers but it will be far more than I could expect from an X pipe even if I don't fully open the cutout flaps. Good cutouts will cost about $450, the welding about the same as an X pipe but I think the cost benefit ratio will be far better than an X pipe.

I love the sound of Dinan exhaust and don't want to change that. Not saying the X pipe is not a significant benefit to a closed exhaust system but since I have not read anything that reported any significant measurable improvement in performance my conclusion thus far is that the cost benefit outcome is not good.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas