Until some-one does independent flow tests of each runner compared to the total flow of each of the six intake ports of the alloy head, then no-one knows. Redline has worked well in the past, but the Ultraflow has some impressive numbers.
I tell you what. Some mainfolds flow huge numbers on there own, but once bolted up to a head with a carb, the total pckage can be awfull. Some runner cfm flows can vary by up to 15%. 4-bbl intakes for sixes are often much worse balance wise than the stock 2-bbl ones, but your running blind until you get flowbench numbers. Any mainfold that looses less than 20 % of the head blow when bolted up, and has less than 5% variance cylinder to cylinder, is a solid gold piece of hardware.
One thing has to be intake runner volume. If you got an aggressive cam, and a big set of primaries in a 4-bbl Holley carb, the bigger runner volume has got to be a minus.
