Neat stuff. Doing some quick reading on VNT's suggests that geometry controlled by engine RPM alone optimizes the boost potential. Yet you've chosen to control vanes via throttle position (with a manual boost controller to limit it).

What do you think the effect would be if crank rotational speed (sensor) was used as the sole input for an electronically controlled actuator for controlling vanes? A mapping or table lookup could be used to create an arbitrary relationship between RPM and vane angle. The idea being to dial in the vane angle that is optimal for that RPM at all times, and it's your right foot that ultimately decides how much fuel goes in to take advantage of the boost. But there would be no direct linkage between pedal and vanes.

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Cheers!
Scott McPhee

1987 300D