On my W-9 engine(405ci) I cant say what the gain would
be because I built it with the dry sump from the get-go
but with just the dry sump I would make 12"hg at RPM
and maybe 1"hg at idle.. if you use both a dry sump
and a vac pump you will most likely need a check valve
to limit the vac level... myself, I dont like to go
above 14"hg