My 84011 (750cfm, vs) on my 355ci drag car went 11.23 @ 120 mph. When I was driving it on the street, with an L82 cam, it went 13.00 @ 100 mph and made 18 mpg, with 3.73 gears. The 4010 series carbs have annular boosters, which help atomize the fuel, and help fuel mileage. The problem with the first generation 4010s is they had a horrible intermediate circuit. They had a lean spot just off idle. The transition to the main circuit was poor. Supposedly, they fixed this about 2 years ago. Haven't tried a newer one, so I don't know if it's any better.
They difinitely have some advantages. No fuel spillage during jet changes, and most the components are standard Holley parts (jets, power valves, accelerator pumps and cams, and needle and seat). There are some special parts, however, such as the float bowls, squirters, and gaskets.
Hope this helps. Take care.
[This message has been edited by 69SSRS (edited 01-19-2001).]