Question for the Motor Heads

[ATAG_Dutch]

No, not Lemmy's gang!

I do have a bit of knowledge about engines and how they work, but an aspect of engine behaviour in CoD is baffling me a bit.

It's my understanding that superchargers are driven mechanically, as opposed to turbos driven by exhaust gasses, so my question is this;

Why is it that when you coarsen the prop pitch and RPM's drop, the boost gauge goes up? Conversely, when you reselect fine pitch, boost goes down?

If driven mechanically, surely supercharger boost should increase with RPM.

Or does a waste gate in the manifold close in relation to prop pitch setting?

Also is the RPM gauge telling you prop RPM or engine RPM?

Any answers or links to articles would be appreciated!

Thanks in advance!