What vac reading are you getting ? Does that gauge measure the full system (. Inc the vacs in the machine) or just the booster?
It does look a well made piece of kit
I really didnt try it much yet , its over 15HG so far , so less than two HD electros .... how ever there is a good blast of air from the exhaust for airflow should be up .
I still have fit a 6.6 to the lower Enforcer vac position to see what four 6.6 is like , there is still one HD electro in there now ... but il leave it til the xmas break as i have to make brackets etc .
It should measure the total HG with both going though