I recall George Braly saying that they had done ground tests, using a
Chadwick-Helmuth vibration analyzer, with and without GAMIs - showing
less vibration at lean mixtures with the GAMIs, several years ago.
This is consistent with the wisdom that running lean of peak in an
unbalanced engine, the cylinders are putting out different amounts of
power - because in this regime the cylinder powers are directly
proportional to the (unequal) cylinder fuel flows.

Ed