I am far from an expert on blowers, but have some basic understanding of them, having messed with one a bit.
If you put a head on that flows ten percent better, and show a large drop in boost, bring the boost back up to 12 lb and the differance should be roughly the same increase in total pressure brought back into the picture.
12 psi boost, plus atmospheric pressure would be 26.7 absolute psi. If you loose 2.67 psi on the head change, then increase the boost back to 12 psi, it might show a 100 hp increase. There are a lot of variables
i don't know about on this type of blower, so take it as a WAG.