Why will a restrictor gain you anything at all?

Im not 100% it wont, but cant see how it can at all.
Seems like a myth to me.

Rally engines are so torquey due to engine spec, not the restrictor.
Unless a rectrictor cures compressor surge which is what enables the cars to run 3.5bar+ or whatever mad boost spike they run, which is of course what gives you torque.

Id love to REALLY know, all i hear is rumours.