Excellent piece of information, i'd never have thought of what they were doing.
If i'm reading it correctly, they were essentially storing energy in the supercharger momentarily and then used it to increase their climb rate in bursts. Planes don't cruise on maximum RPM all the time since the propeller has more "pull" if it's angled to have a bigger "bite" of air, but this also results in increased air resistance/drag and lower RPMs.
So, they were setting high RPMs and momentarily sacrificed some "pull" to speed up the engine and the supercharger, then used the power stored in the supercharger to drive the prop at lower RPMs with higher pull. It's amazing what kind of little tricks seasoned veterans could pull. I guess that each little thing by itself didn't do much, but adding it all up together must have given a tangible performance advantage.
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