Dave
the flow bench uses vacuum to pull air threw the heads. the vacuum is
calibrated in inches of water
the flow bench used in testing uses 28 inches of water as the standard
calibration
the valve sizes on my big valve heads are 42 MM  intakes up from 40 MM and
36 MM up from 34 MM
the head work I have done to these big valve heads is not about hoging out
the ports and loosing air speed. The work I have done on these heads is
about increasing the air flow around the valves.
the reports I have received about the high flow valve jobs to this point
indicate that the low end and mid range power is improved
Bob Donalds
Boston engine
http://www.bostonengine.com