Dominators on the Road
Brian Rock is probably a familiar name to Pontiac readers. He's been on two CC Anti-Tours driving his yellow, 10-second '65 GTO. When setting up the engine and car combination, he contacted Patrick James at Pro Systems Racing for a 4150-style Holley. But because Rock was already using a Dominator-style intake, James suggested a modified three-circuit Dominator. In a recent road test, the Pontiac knocked down 12 mpg and Rock raves about the throttle response.
The trick, according to James, is to integrate the intermediate circuit as a tuning device. "Why give up that adjustability? I'd rather build a four- or five-circuit carburetor to take advantage of that tuning." James requires very specific data from each car/engine/chassis combination and then uses that data to reference previous carb tuning combinations that he has found successful. James recommends going with a Dominator carb only for engines of at least 400 ci and 550 hp. Smaller or less powerful engines, he says, are better off with a smaller 4150-style carb. This is because the Dominator employs such huge throttle blades that smaller-displacement engines cannot handle the Dominator's monster changes in area compared to smaller 4150-style throttle blades.
For street engines, James says the intermediate circuit is worth about 3 to 5 jet sizes worth of fuel at wide open throttle (WOT) and roughly twice that (6 to 10 jet sizes) at part-throttle. This is because the placement of the intermediate circuit outlet (just above the throttle blades) is very sensitive to part-throttle signal, which may be 7 inches of vacuum for example at part-throttle but only 1 inch at WOT. A critical point here is that both the idle and intermediate circuits continue to deliver fuel at WOT. This is important because the common misconception is that the idle circuit goes dormant once the main circuit takes over.
James' recommendations for a guy attempting to tune a Dominator for the street is to start with a broad selection of main jets, idle- and intermediate-feed restrictors, and idle and high-speed air bleeds. Then start tuning with the aid of a wideband oxygen sensor like the Innovate Motorsports unit. Then it's just a matter of being patient and keeping very good notes of the changes you make to keep track of your tuning progress. If you want to take the easy route and have Pro Systems modify your existing carb, the cost is roughly $350 to $400. Or, you can buy a VHS tuning video from Pro Systems for $20 and begin your own carburetor learning curve.
Brian's 10.0:1-compression 427ci Pontiac runs 10.50s at 127 mph on nitrous using a Pro Systems-modified 1,088-cfm three-circuit Dominator carb knocking down decent mileage when combined with a TH200-4R overdrive automatic. | 
This is a three-circuit main body assembly with a brass feed restrictor placed in the third circuit hole (arrow). As you reduce the size of the intermediate feed restrictor, the third-circuit air bleed also needs to be adjusted to match. |
This is a three-circuit metering block. Note the easily identified curved passage (arrow) that is not present in a two-circuit metering block. | |