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Holley Carburetor Line - How It Works

Blane Burnett reveals the latest updates to the Holley Carburetor Line

Stephen Kim Oct 23, 2014
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It's been nearly 20 years since the OEs fully transitioned to EFI, and aftermarket EFI systems are becoming more affordable and easier to tune by the day. Even so, the carburetor remains the fuel atomizing device of choice for the vast majority of hot rodders. Not surprisingly, Holley has remained committed to constantly updating its line of legendary carburetors. Although today's Holleys may resemble the 4150s and Dominators of yesteryear, they have been fully revamped from top to bottom. From adjustable throttle linkages to corrosion-resistant coatings and big-bore venturis to revised metering circuits and integrated idle bypass valves, today's Holley carbs are better than ever. Consequently, we got in touch with Blane Burnett of Holley to get a better handle on all the upgrades packed into a modern Holley carburetor.

Gen 3 Dominator

Originally designed for NASCAR competition in 1969, the racing pedigree of the Dominator carb is unparalleled. Nevertheless, Holley has continued to make improvements to the design over the years, and the latest iteration of the legendary fuel atomizer is the new Gen 3 Ultra Dominator. Among the many improvements compared to earlier Dominators include greater airflow, a new main body, 20 percent larger fuel bowls, and built-in drain plugs. Likewise, the new Dominators utilize boosters with billet 12-hole inserts for superior atomization and throttle-response, as well as a throttle-position sensor mount to keep up with modern data acquisition systems. "The newly patented Gen 3 main body is 5/16-inch taller than previous generation Dominators. This allows for larger radius air entries that deliver smoother flow into the newly machined, big-bore venturii design for predictable and repeatable performance," Blane explains. "The larger 1,350- and 1,475-cfm models now have skirted boosters to ensure a strong fuel signal, and 1x4 and 2x4 calibrations are available for today's larger engines and newer fuels. Furthermore, the throttle linkage is now an external and fully adjustable stainless steel unit. There are no linkage parts under the carb anymore. Other enhancements include all-aluminum construction that's 28 percent lighter, amounting to a 3.8-pound weight savings."

Generation Three Denominator 2 2/16
Generation 3 Denominator 3 3/16
Generation Three Denominator 4 4/16
Holley Carburetor 1 5/16
Holley Carburetor 2 6/16

Adjustable Linkage

Given their racing heritage, traditionally a Dominator's secondaries have opened at a very aggressive 1:1 rate. Depending on road surface conditions, that can make a car challenging to drive on the street and at the track. To make it more adaptable to various applications, the new Gen 3 Ultra Dominator features an adjustable throttle linkage that offers four opening rates for the secondaries. Making adjustments is as easy as removing the secondary link and re-attaching it to one of four adjustment holes on the primary shaft. "Users can easily adjust the actuation settings between soft progressive, intermediate progressive, progressive, and 1:1. When you open all four barrels, you typically have a big pressure drop, so an adjustable linkage can be very helpful on a small cubic inch engine running a large carburetor," says Blane. "Out of the box, the linkage is set up for a 1:1 ratio, meaning that the carb's primaries and secondaries open simultaneously. The opening rate can be changed as need to help the carburetor transition, which technically can help out if you're going to run a Dominator on the street. However, it's mainly designed for more adjustability in a race application."

Generation 3 Ultra Dominator 2 7/16
Generation 3 Ultra Dominator 1 8/16
Adjustable Linkage 9/16

Durable Coatings

Holley's recent carburetor revamp includes an optional gray coating for the Gen 3 Ultra Dominator, Ultra HP, Ultra Double Pumper, and Ultra Street Avenger models. These coatings not only look great, but provide much needed corrosion resistance as well. "We saw a need to develop a carburetor that would stand up to repeated use with the more corrosive fuels that we are plagued with putting through our engines nowadays," says Blane. "The Hardcore Gray coating is a step beyond a good-looking carburetor. It's a hard coat anodizing that will keep a carburetor looking and performing well for many years to come, especially when matched with Holley's billet metering blocks and baseplates."

Metering Circuits

The Gen 3 Ultra Dominator is available with either two- or three-circuit metering. Two-circuit metering features an idle and high-speed circuit, whereas a three-circuit metering adds an intermediate circuit that aids in the transition from idle to WOT. Three-circuit metering is typically used in a race application where the intermediate circuit assists with fueling when coming up on the transbrake. "The intermediate circuit draws fuel through the metering block and air from the bleed in the main body. The air and fuel then join up in a tube that discharges into the throttle bore," says Blane. "A two-circuit carburetor is better for street applications, since the addition of an intermediate circuit can richen up the air/fuel mixture too much. A three-circuit carb is preferable for transbrake applications that need help transitioning between the idle and high-speed circuits. Three-circuit metering can also be beneficial for a manual transmission drag car that's launched at high rpm."

Metering Circuits 2 10/16
Metering Circuits 1 11/16

4150 Models

Although many hot rodders yearn for a Dominator based on intimidation factor and reputation alone, the Holley 4150 is arguably the most popular street/strip carburetor in the world. As with the Dominator lineup, the 4150-series carbs have benefitted from continual revisions over the years. Today, the 4150 model line includes Classic, Street, and Ultra HP. "Holley's Classic 4150 series carburetors are characterized by traditional zinc fuel bowls, metering blocks, and main bodies. Ranging in flow from 390 to 1,000 cfm, the 4150 Classic features contoured venturi inlets, high-flow metering blocks, Dominator-style fuel bowls, screw-in air bleeds for precision tuning, progressive secondaries, notched float and jet extensions, stainless throttle plates, and race-calibrated tuning," Blane explains. The Street HP, in contrast, combines the features of a race 4150 and a double-pumper to create a versatile street/strip carb. "The Street HP utilizes a street calibration similar to a double-pumper, and unlike a race carburetor it features vacuum ports. Street HP carbs have dual accelerator pumps, contoured venturi, four-corner idle control, and a vibratory polished finish. Finally, the Ultra HP has much more adjustability, and boasts many of the latest updates to the 4150 line."

Ultra HP 4150

If you put together a wish list of everything you wanted in the ultimate carburetor, the result would be the Ultra HP 4150. Available in configurations ranging from 600 to 950 cfm, the Ultra HP utilizes a billet aluminum baseplate and metering blocks for enhanced durability and gasket sealing. Furthermore, the Ultra HP has a dual bolt pattern for full compatibility with both 4150- or 4500-style intake manifold flanges. To improve airflow, the air bleeds have been moved outward and the squirter screw heads are streamlined, while an integrated idle bypass valve improves idle quality when using large camshafts. The Ultra HP's fuel bowls are 20 percent larger and include an integrated drain plug. Also, the secondary throttle linkage is now adjustable and knurled curb idle screws allow making adjustments without hand tools. There's more than meets the eye, however, as the Ultra HP is loaded with details that aren't visible upon first glance. Inside the fuel bowls are a series of fuel troughs, baffles, and shelves designed to reduce slosh and aeration. A cap on the primary throttle shaft seals it off from debris, and all-aluminum construction reduces weight by 38 percent. The needle-and-seat area, fuel inlet, and sight windows are beefier to better survive harsh racing conditions. There are even pry points built into the metering blocks to prevent damaging the gasket surfaces. To top it all off, the Ultra HP comes in either a shiny or Hardcore Gray anodized finish. "The Ultra HP offers a level of performance and adjustability never before seen in a 4150 carburetor," says Blane.

Choked 4150 Models

For cars that will see a lot of street action and can benefit from a choke assembly, Holley offers two variants of the 4150 carburetor called the Double Pumper and Avenger. "On a Double Pumper model carburetor, there are mechanical secondaries and two accelerator pumps. Street Avenger carbs have vacuum secondaries and a single primary accelerator pump," says Blaine. Mechanical secondaries are often used in lightweight vehicles with manual transmissions, or automatic-equipped cars with high-stall torque converters. Conversely, vacuum secondaries work extremely well in heavy cars. Both carbs can support plenty of power, as they're available in configurations exceeding 800 cfm. Likewise, the Double Pumper and Avenger can be had with either manual or electric chokes, and in a choice of zinc or polished finishes.

Holley 4150 Carburetor 12/16
4150 Model Carburetor 13/16

E85 Carburetors

The wide availability of E85 in certain parts of the country have prompted many hot rodders to make the switch to the popular alcohol-based fuel. However, the tuning calibration changes necessary to convert a carb to E85 aren't always clear-cut. Fortunately, Holley has eliminated the guesswork with the introduction of its E85 carbs. "Holley's E85 Ultra HP carburetors have newly calibrated metering blocks, stainless steel needle and seat assemblies for corrosion resistance, and high-flow power valves necessitated by the greater fuel volume demands of E85," Blane explains. "They also utilize a Viton GFLT diaphragm that's alcohol compatible. It's essentially a fluoroelastomer with a wide-range of fluid resistance and low temperature flexibility. Additionally, Holley invested a great deal of calibration time with the metering blocks to ensure that the air/fuel ratio is spot on given the requirements of E85."

Booster Design

Holley carbs are offered with both annular and down-leg boosters. The particular style of booster used in a given application is dependent on the carb signal produced by each engine combination. "Annular boosters are better suited for improved low-end to mid-rpm atomization on a vehicle that doesn't have a lot of signal, whereas a down-leg booster works well in a mid- to high-rpm range where you have a good signal draw," says Blane. Generally, the greater a booster's restriction to airflow, the greater the signal. "The carb signal refers to how hard the engine is pulling air into the carburetor, and is sometimes referred to as pressure drop."

Booster Design Application 14/16
Booster Design Carburetor 15/16

Wet Flow Testing

Holley carbs are wet flow tested prior to shipment. That sounds great, but what specifically does this type of testing entail? "Flow testing ensures our carburetors meet correct calibrations and will perform as expected in the field," Blane explains. "Every Holley carburetor is based off of a master carb that was developed at the beginning of the production process. We test each new carb against the target numbers provided by the master carb to ensure something hasn't gone awry during the production phase. It is simply another way of providing customers with a carburetor that works great out of the box with little to no tuning in most cases."

Custom Tuning

Carb tuners often talk about flattening out the fuel curve to each engine combination. In other words, the goal is to provide consistent fuel flow throughout an engine's operating range, and Holley's wet flow testing goes a long way to ensure that they perform extremely well for the vast majority of engine combinations straight out of the box. According to Holley, however, once camshaft duration exceeds 250 degrees of duration at 0.050, engines become much more finicky and may benefit from custom tuning. "Whether or not a carb can benefit from custom tuning depends on the type of application the carburetor will be used on. Race and street are totally different," says Blane. "We try to release carburetors that will work well across a wide range of applications, but there is a reason why carb modifiers exist. Some radical engine combinations will inevitably require some tuning once installed."

Holley Carburetor Custom Tuning 16/16

Fuel Additives

In addition to ethanol, modern fuels have lots of additives that are often detrimental to fuel system and carburetor performance. Recognizing this problem, Holley has developed several methods of combating the downsides of modern fuel. "On the carburetor side of the fuel system, Viton GFLT pump diaphragms and Hardcore Gray anodized coatings are very effective in battling corrosion," explains Blane. "As for the fuel system itself, PTFE hose is highly recommended. Alcohol is a moisture wick, and it tends to pull moisture out of the air. With that in mind, you have to make sure to flush the carburetor and drain the fuel bowls if you're not going to be using the vehicle for a week or two."

Terminator EFI

Holley's legendary line of carburetors aren't the only fuel mixers receiving updates. "Those interested in Terminator EFI can expect some upgraded packages in the coming months that will support higher horsepower levels, as well as blow-through supercharging, and more. A great way to find out about these upcoming products and more from Holley Performance is to sign up for our monthly Gearhead Newsletter at www.holley.com," says Blane.


Holley Performance Products
Bowling Green, KY 42101



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