This is a 750-cfm Dominator on Dave McClelland's street-driven 454-powered '55 Chevy. With plenty of image going for it, it still offers decent driveability despite its out-of-the-box tune-up. This Rat even sports air conditioning and Dave reports no problems with throttle response or driveability. | 
Original Dominators came with these single-discharge-port boosters that are very lazy. If you have one of these carbs, the smart move is to exchange these boosters for an annular-discharge version. |
This is a 750-cfm Dominator booster that is easily identified by the flare at the bottom of the booster (arrow). This configuration creates a smaller venturi area and increases the booster's responsiveness. | 
Dominator boosters are easy to change. Use an easy-out to remove the booster pins and then merely swap the boosters. |
Dominator ID
Besides the cfm rating, Dominators come in either two- or three-circuit configurations. A two-circuit Dominator refers to the idle and main circuits. The three-circuit Dominators include an intermediate circuit that was originally intended to add additional fuel for radical race engines in the transition between the idle circuit and the onset of the main metering circuit. This was done because many competition engines operate with such low manifold signals at slow speeds that this circuit became necessary.
According to Murphy, out-of-the-box three-circuit carbs are generally overly rich for street use and not a good choice. If you are swap-meet cruising for a used Dominator, the best bet is to avoid the three-circuit carbs because they can produce a very rich off-idle mixture in stock condition. However, these can be made to work if you're willing to do some dedicated tuning on the carburetor, or SMI can perform the necessary tune up.
Above: The best way to identify a three-circuit Dominator is to look for the small fuel-discharge port located below the booster and above the throttle blades (arrow). Right: Three-circuit carbs also use a third air bleed for each venturi, but SMI warns us that a few weird three-circuit Dominators used an internal air bleed placing only two bleeds on the top of the venturi. This overhead view of a three-circuit Dominator reveals the location of the idle air bleed (A), the intermediate air bleed (B), and the high-speed air bleed (C). |  |