Fruit Loops and Carb CFM Ratings

[Qikbbstang]

The 11/2012  Circle Track has an article comparing the 950 Holley HP and  Holley's new Ultra HP carbs.  They flowed 1044cfm and 1139cfm respectively at 23 inH2O.  I was thinking about the 23inches vac. figure, that they chose to test at. Being in filter industry I'm used to seeing SCFM ratings in tests performed under the various authorities guidelines but 1000cfm is a lot of air.  To me the best way to see 25" inH2O from a motor is to rev it up and slam shut the throttle. Vacuum that low it's almost non-existant in a normal motor and certainly never seen at WOT.. So why do they test carbs at such extreme vacs?.............................
 I can only guess they may also use high vac figures when test flowing intake manifolds and heads.  Do the charactoristics of flowing air under low and high vacuum levels stay proportional in how smoothly it flows?............................
 I'd expect a port on a flow bench may flow smoothly up to a given cfm and then start buffeting, but unlike a flow bench the dynamic vacuum in a real motor may never be capable of pulling near as high cfm figures to get to where the buffeting in the ports occurred on a high vac flow bench.   So a port design that falls apart at high cfm on a flow bench may be miles from seeing anything near that cfm in operation.   
 I also wonder about the mass of a gas stream (which suspends droplets) changing under vacuum which I presume effects wet flow.. 
           

[Chad D]

I thought the SAE delta pressure was 20.4"/H2O or 1.5"/Hg for four barrel carbs, and 40.8"/H2O or 3"/Hg for two barrel carbs... 

23"/H2O is 1.7"/Hg.  Is this manipulation for salesdroid's sake, or is there specific application information that we're missing?

[jayb]

I thought the SAE delta pressure was 20.4"/H2O or 1.5"/Hg for four barrel carbs, and 40.8"/H2O or 3"/Hg for two barrel carbs... 

23"/H2O is 1.7"/Hg.  Is this manipulation for salesdroid's sake, or is there specific application information that we're missing?

1.5" of Hg and 3.0" of Hg is the standard.  My guess is that they tested at a higher pressure drop on the carbs for marketing purposes.  Gotta read the fine print...

By the way, if your motor is EVER pulling 1.7" of Hg at WOT, you are seriously undercarbed...

[Chad D]

So, corrected to SAE specs, 983 cfm for the HP, and 1073 cfm for the Ultra HP.  Revealing myself to be a plebe on this much farther, is there any data out there on FE heads that actually measure pressure drop and velocity on a running engine that has been shared?