That's the cfm conversion from 2barrel to 4 barrel flow rates.
You can flow a lot of air if you like, but, if the manifold is not good (cough cough 6 pack cough) it won't make power it should. The manifold is a real bottleneck.
I don't have any information on the small block intake, but I was told that the RB sixpack intake doesn't make a lot of power either. After actual dyno testing, I found this to be a myth. My previous Edelbrock sixpack intake flowed enough air to produce nearly 700 hp, and makes more power than a fully ported Victor 4bbl Intake and both a 950 & 1050 cfm Dominator in the mid-range and only a handful of hp less on the top-end.
My current sixpack manifold has since been massaged even more internally, and the motor altered slightly(bigger solid roller and 10.2 compression), but I have not gotten the car back on the dyno yet.
