The basic design of a carburetor is well over a hundred and twenty five years old, as invented by the founder of Mercedes-Benz in 1885. Although they have long been superseded by EFI in passenger vehicles, carbs are still widely used today in street/strip and racing applications.
Nothing beats the carb for ease of use and quick tuning, and they have not stopped evolving, as the most recent addition to the carburetor evolutionary ladder offers some really exciting new features.
Super lightweight, better tuning.. and an all-aluminum body and base plate.
Welcome to the Holley Ultra series.
Holley’s Jump Into Aluminum Bodies With the Ultra Series
The biggest achievement with the new Ultra line is Holley’s foray into the aluminum body market while previous generations were made from zinc. Zinc itself is a bright silver-like metal, and the problem with untreated zinc is that it reacts with air and water to make a powdery material known as ‘white rust’. The green of the typical Holley carburetor actually comes form a chromic acid solution, which forms a thin layer on the surface of the metal and helps protect the surface.
Holley’s jump over to aluminum bodies was much more involved than you would think. “The characteristics of a zinc body is completely different from an aluminum body,” says Jay McFarland of Holley. “We had to completely redesign the carburetors from the ground up. Nothing really changed, it was just compensating the design for how the aluminum pours and reacts versus how the zinc does.”
New Carburetor Design Receives a New Tune Up
Holley has always done a great job with the out-of-the-box performance on their carburetors. Regardless of application, they will generally get the car running and idling correctly and offer a safe fuel curve under calibration. Generally, one would find themselves dropping jet sizes down a little since the stock calibration is a bit on the safe side. With the Ultra series, these carburetors received 100% fresh-tune set-ups.
“One thing we did with the Ultra Series is that we completely went through and re-calibrated all the fuel curves on them,” commented McFarland. “This allows for better throttle response and drivability. When the double pumpers were first released in the late ’60s, that had a little richer fuel curve to them. Over the years we have learned a lot from them and that allowed us to tune them in a little better.”
Holley re-calibrates their carburetors in three different ways:
- Flow Bench Testing
- Engine Dyno Testing
- Real World Vehicle Testing (with wide band 02 sensors).
This ensures that the tune up will be more aggressive than years past, but not too aggressive to cause problems. You wonder, how much? Holley says around 5-15% leaner, depending on the carburetor.
Additional Options on the Ultra Series
While the Double Pumper and Avenger carburetors received mainly aesthetic and weight changes, the Dominator’s received some performance enhancements. The main difference between these two street carburetors is that the Avenger operates with vacuum secondaries and the Double Pumper is mechanical. Also, before the Ultra line, the Double Pumper did not have an electric choke, though it now comes with one.
The weight savings on the street carburetors is five pounds while the Dominator drops nearly four. Also, the street versions are offered in blue, red, and black accents while the Dominator only comes in red or black. “Another great thing about the aluminum bodies is that they are very easily polished. You can do a hand polish on them and almost make it look like chrome,” said McFarland.
Billet Metering Blocks and Base Plates
Another cast component that takes the kick to the curb is the base plates and metering blocks. In it’s place, you get fully machined billet components offered in red, blue, or black. Since the Dominator’s have integrated base plates (which are aluminum now), the billet versions are only available for the Avenger and Double Pumper. The billet base plates won’t snap if an over-tightening situation occurs, and they also will never deflect over time and lead to vacuum leaks. The billet metering blocks allow for a true mating surface between the main body and bowls to prevent leaks. Also since the metering blocks are billet and not cast, porosity problems will be a thing of the past.
Making sure your float bowls have the proper amount of gas in them is important when it comes to ensuring a properly running carburetor. Too much fuel in the bowls will push additional gas into the carburetor and too low will cause the car to stumble as they run dry. If you are trying to reduce the float level while the car is running, this can cause fuel to pour out of the side of the carburetor and onto a hot engine. Temporary plastic sight levels will get smoky if you leave them installed. The glass levels allow you to quickly check the level and adjust it without spilling any fuel.
Further Performance Enhancements on the Dominator
The billet metering blocks in the Dominators offer more fine tuning options. They come with changeable idle feed restrictors to change idle air/fuel ratios, changeable emulsion bleeds to help with fine tuning, and tunable power valve restrictors for smoother fuel transition to the main circuit.
Previous generation Dominators had an internal throttle shaft when it came to changing the rate of opening on the throttle blades. These were time consuming to adjust and contained moving parts that racers feared could come apart and fall down into the intake manifold. They have been simplified by a new external linkage design that allows for a 1 to 1 or progressive opening. The linkage has different selector holes for changing the opening speed and can be fine tuned with the adjustable linkage.
Rounding out the additional benefits includes teflon-coated slabbed throttle shafts with lower profile screws for improved airflow, hand polished venturi inlets, and 12 hole billet booster inserts to allow for better fuel atomization plus crisp throttle response.
Installing a 750 CFM Ultra Double Pumper
If you have been following Street Muscle, you might have seen our Project: Riced Rat Rod 240sx. The stock fuel injected 2.4-liter has been yanked in place of a 400ci Dart SHP short block with Pro 1 Top End Kit. This light 5-speed equipped car makes 525 horsepower at the crank with a Holley 830 CFM HP carburetor. With an Ultra 75 CFM Double Pumper on hand, we wanted to see how it compared to the 830 HP.
Swapping the carburetors couldn’t be easier.We started by cracking the -8AN line at the regulator and soaking the fuel up with a shop rag. From there we removed the quick disconnect throttle bracket and return spring. Finally, the carburetor was set free by removing the four base plate mounting bolts.
Before we installed the Double Pumper we wanted to see what it weighed compared to the HP. The Ultra Double Pumper came in at about three pounds lighter, and don’t forget that the Double Pumper has components like the electric choke and choke tower that adds extra weight over the HP.
Reinstallation of the Ultra Series carburetor was just as simple as taking it off. The only other item we needed to add was a switch 12 volt wire for the electric choke. As the small block Chevy came back to life again, we were greeted with a healthy sounding idle thanks to Holley’s out-of-the-box tune.
Concluding our driving test, we found that the cold start idling did not require us to sit with the car for a few minutes while we warmed it up. Also, we were pleased to note that the partial throttle drivability was enhanced. The 830 HP performed with slightly crisper throttle response and more ‘seat of the pants’ horsepower above 5,000 rpm. The tough decision comes down to determining exactly what you are looking for out of your vehicle.
Project Grandma – Testing the Ultra Series 3-Circuit Dominator
Since we tried out one of the street carburetors on one of our street cars, we decided it would only be fitting for us to try out one of the Dominators on one of our race cars. The lucky vehicle that will be undergoing this test is Project Grandma, our 555 cubic inch Musi/Edelbrock big block Chevy-powered Malibu.
The carburetor of choice is the 1050 CFM 3-circuit version. While 3-circuit isn’t really designed for a street car, it will work perfectly for our Malibu that only spends its time at the track. The extra circuit adds an intermediate circuit between the idle and main. This allows us to adjust the carburetor’s intermediate circuit to tune the air/fuel ratio on the transbrake for a crisp delivery to the main circuit when the button is released. This will keep the car from bogging while on the trans-brake when releasing it.
Even though the Ultra line was a significant revelation to Holley’s line of carburetors, there are plans to continue pushing still further. “Look for more to come soon,” McFarland told us. “We plan on expanding out into the bigger CFM on the street carburetors – including a 570 and 870 Avenger as well as 600 and 850 Double Pumpers.” Both of these CFM ranges will be offered in both the standard zinc and Ultra line of aluminum carburetors.