Put a paper clip on the dashpot rod and take it for a drag. See how far the paperclips have slid on the dashpot rod. If its set up correctly for that motor, I guess they are gonna open. An 8bbl has way less vacuum across its openings so the CFM is not doubles, but its a factor of like .6 or something. Vizard has a graph that showed the cfm through a 6 pack (1350?) was closer to 990 with a 440 pulling on it and the line went down as the CFM got lower. I think its somewhere posted by me in teh massive FABO database.
