All the old BG Demon carb ratings were established by wet flow testing, with all 4 barrels wide open, at 1.5" Hg./20.4" h2o.
When fluid is introduced into an airflow rig, the test pressure will increase 2" h2o per Joe Mondello- who also used a wet flow rig to flow heads. Reher/Morrison obtained a Mondello CFM-WFB2000 freestanding wetflow bench from Mondello. They pulled 28" h20 at 1" valve lift on one of their R&D Pro Stock heads- and stated they gained vast amounts of knowledge in very short time using the Mondello flow rig.
What this means is, if the flow bench is on stable at 28", and the fluid is turned on, the flow pressure climbs to 30". Then it has to be turned back down to maintain 28" with wet flow on. The same phenom would occur when BG was flowing his carbs.
If you then took those BG carbs, or Mondello heads, and flowed them dry, they'd flow a higher number than when they were flowed wet.
an 825 Demon could flow around 865 cfm on a dry bench at 20.4"
if it was put on a 28" bench, it could flow around 965 cfm.
BG flowed the carbs complete all 4 barrels open with that huge flow bench,
so the effect of the inlet bowl scalloping could be measured accurately.
other carb companies were flowing only one barrel, then multiplying by 4 to get a number. or flowing the front half of a 4bbl, and multiplying by 2.
that doesn't take into account the choke horn, or removal of it, scalloping, etc.
if the Edelbrock VRS line of carbs is being flowed dry at 20.4", or at 28", that would explain the ratings they are being given.
|