The early 90° V twin Moto Guzzi's (750 cc and up) had a balance pipe between the horizontal sections after the downpipes and before silencers. The 850 Le Mans also had this, but sported another balance pipe welded between the two downpipes such that they formed a single assembly. I always understood the mutual exhaust pulses improved scavenging between cylinders.

I remember Krazy Horse developing similar for their Stage 3 converted M3W as below.

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