Dominators are massive and flow a ton of air, but otherwise they're just an oversized Holl
`Let's start this story with the disclaimer: A 1,050- or 1,150-cfm Dominator on the street is usually not a good idea. Unless you're packin' at least 400 inches and 550 hp, a Dominator is not the carb of choice for a streeter. These are cavernous carburetors that will sacrifice throttle response and off-idle driveability in favor of max airflow. So now that we've just convinced you that you must have a Dominator, we'll let you in on a few tuning secrets that can turn a fat, lazy 4500-series carb into a respectable fuel mixer.
To help us navigate around the big, bad Dominator, we hoofed it over to Sean Murphy Induction (SMI) where Sean gave us a guided tour through this big carb maze.
We'll break this carburetor down into individual sections to make it easier to understand the modifications that need to be made. The bottom line is that large carburetors can be made to work on the street. The choice is to either invest in a custom-built carb modified by a professional carb builder like SMI or spend the time, patience, and money in search of the knowledge and tricks to modify your own carburetor to perform up to current expectations. None of this will come easy and there's much more to the Dominators than we could cover here. If you do your homework, you can make a Dominator work on the street. Just consider yourself warned.
What's a Dominator?
Holley originally produced the Dominator carburetor in 1969 exclusively for Ford NASCAR and Trans-Am engines. Later, Holley made them available for other competition uses and they instantly appeared on high-winding small-blocks in NHRA Pro Stock racing. All Dominators use 2-inch throttle plates except for the new 1,250-cfm Dominators that employ bulbous 214-inch throttle blades bringing the total sizes to four: 750, 1,050, 1,150, and 1,250 cfm. Besides the skirted booster used in the 750, the only difference between the 750, 1,050, and 1,150 is the 1,150's larger venturi (11316 versus 11116).
Holley refers to this carb as the 4500 series, differentiating them from the smaller, square-flange 4150/4160 carbs. Dominators use a much larger carb flange, which demands its own intake-manifold mounting flange. Of course, you can use an adapter/spacer to run a 4,500 on a 4150-style manifold, but this often results in poor mixture distribution unless the adapter is custom fitted to the intake.
The idea behind the Dominator is obviously to flow large quantities of air. But velocity also plays a part in the carburetion game, which means a larger flow path also slows the air down through the carburetor. This is often a benefit for high-rpm drag-race applications. Slowing the air down through the carburetor allows the heavier fuel particles to make the difficult 90-degree transition into the individual inlet ports. For a street-driven engine, it is this same large airflow path that is the reason behind less-than-crisp throttle response and rich mixture tendencies that are typical of the 4500-series carburetor.
This is a 750-cfm Dominator on Dave McClelland's street-driven 454-powered '55 Chevy. With
Original Dominators came with these single-discharge-port boosters that are very lazy. If
This is a 750-cfm Dominator booster that is easily identified by the flare at the bottom o
Dominator boosters are easy to change. Use an easy-out to remove the booster pins and then
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-di
Fat Idle Fix
You might not realize it, but a street engine spends a majority of its life between idle and cruise mode. This activity is all controlled by the carburetor's idle circuit. Within this circuit, the combination of the idle-feed restrictor, the idle-air bleed, and the idle-mixture screw establish the maximum amount of fuel delivered by the idle circuit. Of the two fixed restrictors, the idle feed is the most important. A typical Holley 750 double-pumper 4150-style carburetor is generally fitted with an idle-feed restrictor of 0.034 inch, an 850 will have a slightly larger 0.037 inch, and the idle-air bleeds will measure between 0.067 and 0.070 inch. Most Dominators are fitted with much larger 0.041-inch idle-feed restrictors. This may not seem like much, but you would have to reduce the 0.041 restrictor by 31 percent to equal the area of the 0.034 restrictor. If you want to do the math, remember that area is Pi (3.1417) times the radius squared. This means the
Dominator's idle circuit has a flow area almost one-third larger than a typical 750 4150-style carburetor, which is already a somewhat rich idle circuit for many street engines. The Dominator is so fat because it's intended to be used on competition engines with minimal idle vacuum. On a street engine, the cam will be less aggressive with more idle vacuum and will "pull" more fuel from the idle circuit. This means the idle-feed restrictor must be reduced to return some control over the idle circuit. For example, we offered Murphy the challenge to tune a theoretical 450-460ci street engine with a single-plane intake and a cam with 250 degrees of duration (at 0.050) in a relatively heavy 3,600-pound car with a 2,800-stall converter and 3.73 gears. Murphy suggested reducing the idle-feed restricted down to around the 0.037-inch size while the idle-air bleed should be opened up to around 0.076 inch. Notice he's matching idle-feed and idle-air-bleed changes. Both of these steps are intended to lean out the idle circuit in an attempt to improve off-idle driveability. This can then be a starting point for additional tuning when accompanied with input from a wideband-style air/fuel ratio meter like the one from Innovate.
Holley HP carburetors and Dominators move the idle-feed restrictor from its normal locatio
A quick way to reduce the size of a large idle-feed restrictor is to use a small-diameter
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 Sys
This is a three-circuit main body assembly with a brass feed restrictor placed in the thir
This is a three-circuit metering block. Note the easily identified curved passage (arrow)
All King Demon carburetors are three-circuit designs. For better street manners, this will
The Demon Tweaks
To address the King Demon side of the carb world, we called the company's carb specialist Doug Schriefer. Barry Grant makes a total of six streetable King Demons ranging in size from 795 to 1,295 cfm. One advantage of the smaller King Demons, according to Schriefer, is that the venturi on the 795-cfm carb is a smaller 1.500-incher with the throttle blades a smaller 1.800 inch. These smaller dimensions combined with an annular-discharge booster create higher inlet velocities that make this larger-flange carb more responsive to throttle and somewhat easier to tune. The 895-, 995-, and 1,095-cfm models follow a similar path with increasingly larger venturis and throttle-blade diameters to maintain this velocity.
Schriefer's first suggestion for making any King Demon more streetable is to add a power valve to the primary side of the carb, which allows you to lean the primary by eight jet sizes. This helps driveability and fuel consumption. The King Demons also come stock with screw-in idle-feed and idle-air bleeds, which makes modifying these pieces much easier.
Another important point that addresses any carb tuning is that the idle-feed restrictor and the idle-air bleeds are intended to work in combination. This means that major changes to one bleed should be accompanied by a change to the other. For example, if you are planning to lean out the idle-feed restrictor by making it smaller, it's a good idea to increase the size of the idle-air bleed as well. This also leans out the idle circuit by adding more air. To enrich the idle circuit with an air bleed, you make it smaller. Schriefer's recommendation is to start your tuning exercise with the idle-air bleeds just because they're easier to access. If you are making major changes, a 0.001- to 0.002-inch change to the idle-feed restrictor should be matched with a 0.006- to 0.008-inch change to the idle-air bleeds. If you find you are making very large changes (0.020 inch or more) consider that there may be other problems leading you to such a radical change. END
Let It Bleed
All Dominator and HP carburetors use standard No. 10-32 UNF threads for the idle-, intermediate-, and high-speed air bleeds. This chart lists the specs for the three current Dominator carbs. A full list of Dominator bleed diameters is listed in the current Holley catalog. Holley offers these bleeds in thousandth-inch (0.001) increments from 0.023 to 0.078 in packages of 10.
Idle High-Speed Idle Carb Air Air
Fuel750 cfm (80186-1) 73 36 351,050 cfm (8082-2) 71 37
281,150 cfm (7320-1) 53 28 28
DESCRIPTION PN SOURCE PRICE
Dominator HP 750 cfm, Holley 0-80186-1 Summit $659.95Dominator HP
1,050 cfm, Holley 0-8082-1 Summit 675.95Dominator HP 1,150 cfm,
Holley 0-7320-1 Summit 769.88Ultra Dominator, 1,050 cfm, Holley
0-80672 Summit 1,039.95Ultra Dominator, 1,150 cfm, Holley 0-80673 Summit
1,199.95Annular booster (4), Holley 34-9 Summit 61.88Booster pins
(10/pkg), Holley 20-110-10 Summit 25.39Linkage, soft
progressive, Holley 20-20 Summit 15.88Air bleeds (10/pkg), one size
126-xx-10* Summit 25.99* Replace xx with required size between 23 and
78 `SOURCESDemon Carburetion; Dahlonega, GA; 706/864-8544; barrygrant.com
Innovate Motorsports; San Juan Capistrano, CA; 949/388-4442; innovatemotorsports.com
Pro Systems Racing; Spring Lake, MI; 727/490-5717; pro-system.com
Sean Murphy Induction; Huntington Beach, CA; 714/842-1881; smicarburetor.com
Holley Performance Products; Bowling Green, KY; 270/781-9741 (tech); 800/HOLLEY-1 ext. 8530 (nearest dealer); holley.com
`A cubic yard of air weighs 2 pounds at sea level.