OneBad
You are hitting the NAIL on the HEAD...........
I have seen so may blower motors choke on the dyno because of the limited capability of air intake when using the incorrect sizing of carbs..
When you fire them up you can actually hear the motor trying to breath & it just can't.
I can't tell you how may blower motors I have worked on that have incorrect carbs on them. Its amazing. Its my opinion that a lot of guys, by the time they are ready to purchase carbs are so tapped out of capital to finish their build that they purchase what they consider a reasonably priced set of carbs for their build based off the information from an inexperienced sales rep on the other end of the phone line...
In the back of their mind they are thinking I still have to buy plumbing, regulators, fuel pressure guages, braided line and fuel pumps. It's quite a heavy burden for the budget builder who's looking to tear up the streets or have thier day at the track...
Bottom line is; "Most guys just don't know", but thier ride looks bad as all get out with dual carbs & that massive blower sticking out of the hood.....
I had a similar build on a 515 BBC on Pump Gas 8/71 and only 5 lbs boost. With a healthy set of Jimmie Evans blower carbs on the motor I produced 789 hp @ 7400 rpm, I jerked the carbs off and swithced the motor over to injection , 851 hp at 7200 rpm. Go Figure...