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The way I understand how the DISA valves are working, they are changing the shortest path between the two cylinder banks: cylinder 1,2,3 and cylinder 4,5,6.
Each time the cylinder intake valve closes, this causes a back air pressure wave generated. Similar phenomenon like water hammering happening at water pipes that has sudden closing valves.
Since inline six is balanced, for each cylinder on bank 1 closing its intake valve, there is a corresponding cylinder on bank 2 opening its intake valve. By providing a path from bank 1 to bank 2 at the intake this back wave pressure is directed to fill the other cylinder opening its intake, allowing more air to it.
At low RPM, the connecting path from bank 1 intake valves to bank 2 intake valves is through the pipe where the intake throttle body is screwed in. Both DISA valves are closed. At low RPM, each cylinder valve closing to next opening takes long time (relatively), so they made this path long enough for air wave to flow through that path matching low RPM speeds.
At mid RPM DISA 2 is opened, which provides a shorter path between bank 1 and bank 2 for the back air pressure wave to travel. Now it takes shorter time for that wave to reach the other bank, and that matches with the speed of the valves opening.
At higher RPM DISA 1 is also opened, which provides the shortest path between bank 1 and bank 2, for the same reason, so that the back pressure wave from intake valve closing in one bank reaches just at the right time to the other bank when intake valve opening on the other bank. If it was still using the longer path, air wave would be late now arriving at the other bank.
Question how much is the back pressure pulses that would be acting on the DISA flap with the SC boosted air. I would think with higher air flow, the back pressure generated due to closing of the intake valve will be higher too.
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