The advent and the utilization of the carburetor on internal combustion engine powered automobiles can be traced back as far as the mid 1890’s in England, and throughout the 60-year history of the sport of drag racing the hot rodding movement that preceded it, the carburetor and racing have inextricably linked to one another. Over the course of those six-plus decades, the high performance carburetor has undergone countless innovations and refinements as horsepower demands have increased and the technology has developed, and albeit with the same operating premise, the racing carburetor of today certainly isn’t your grandfathers’ carburetor.
With that in mind, we set out to pick the brains of a handful of the most renowned manufacturers and individuals in the industry in order to take a closer look at some of those innovations and refinements that have taken place over the last decade and culminated in the state-of-the-art race carburetors that are available today.
That first carbureted engine, developed by Englands’ Fredrick William Lanchester and his brother, produced just 5 horsepower from it’s single cylinder design: the same amount of power the carbureted lawnmower in your shed produces. Carburetors were the primary method of fuel delivery for most U.S. made gasoline-fueled engines in production until the late 1980’s, and while the carburetor has long-since been replaced on readily-available production vehicles worldwide, their use continues to this day in the racing world. And it’s through continual research and development of elements such as the fuel bowls, boosters, venturi designs, and other methods for producing greater air flow and fuel delivery that have kept the age-old concept viable in a world where every horsepower counts.
Among the collection of manufacturers leading the technological charge into the 21st century of carburetor technology is a virtual who’s-who of names in the industry. These include the Bowling Green, Kentucky based rivals of Quick Fuel Technology and the historic and iconic Holley Performance Products, along with race-minded Pro Systems based in eastern Michigan, and Advanced Engine Design (AED) in Richmond, VA.
Because these companies and the talented individuals behind the scenes are the true experts on the subject, we allowed them to do the talking as they shared with us their insights and their contributions to the advancement of carburetor technology since the turn of the century, all compiled here into one informative resource.
Holley Performance Products
Look up the word “carburetor” in the dictionary and you’ll probably find a picture of a Holley double-pumper. No name is more synonymous with the carburetor than Holley, and it’s hard to dispute their position as the leader in the industry as their designs have been the standard for more than half a century, with many of their competitors basing their products off age-old Holley designs to this day. And 106 years after it’s founding, Holley Performance still has some tricks up their sleeves.
Holley's Ultra HP carburetor incorporates several new advancements, including a new idle bypass system that's designed to allow for additional air flow through the carburetor while maintaining the relationship between the throttle plate and the transfer slot. The fuel capacity within the bowls has also been increased by some 17% by physically lengthening the bowls 1/8-inch.
Holley keeps in tune to public “wishlists” and commonly compiles that information over time to incorporate in a single carburetor release, such as their Ultra Aluminum HP.
As has become more common in the business, Holley has shifted the manufacturing of many of their carburetor lines over to an all-aluminum construction, while also focusing on other refinements that create an even greater product. One of those being their new idle bypass system design.
The idle bypass is designed to allow for additional air flow through the carburetor while maintaining the desired relationship between the throttle plate and the transfer slot: a great feature on engines with beefed up camshafts. Their older HP units featured holes in the throttle plates to achieve this, which weren’t adjustable. Not so anymore.
To finely tune the newest HP model, a screwdriver is supplied with the kit that one can make can make infinite adjustments to the idle bypass circuit to get the most out of their carburetor.
Holley's new Ultra HP carburetors, available in a natural tumble-polished aluminum and all-new Hard Core Gray finishes.
“That’s something that has really helped out to get more flow through the carburetor. That’s kind of a big deal for us,” exclaimed Holley’s Blane Burnett.
Another area that Holley has addressed has been the fuel bowls in order to allow the user more control over the fuel flow. The fuel capacity within the bowls has been increased by some 17% by physically lengthening the bowls 1/8-inch. To that end, a a new design within the bowl featuring internal baffling also helps to stabilize the fuel and minimize “slosh” that’s a common problem amongst previous models and designs. Also within the bowl, they’ve designed a “shelf” positioned on the backside of the bowl that eliminates aeration and further minimize fuel slosh within the bowls. In earlier bowl designs that lacked such a design element, fuel was being pushed away from the jets, hindering the performance and consistency of the carburetors.
Holley's release of their Ultra Series carburetors last summer features multiple refinements to their legendary models, inlcuding the 4150-style Ultra Avenger, the 4150-style Double Pumper, and the 4500-series Ultra Dominator.
Holley made their first foray into aluminum construction last summer with the release of their new Ultra Series carburetors, which included the 4150-style Ultra Avenger, the 4150-style Double Pumper, and the 4500-series Ultra Dominator. And despite being tried and true names in the Holley lineup, the Ultra Series release signified a host of tuned-up features for the legendary carburetor manufacturer.
“One thing we did with the Ultra Series is that we completely went through and re-calibrated all the fuel curves on them,” commented Holley’s Jay 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.”
Among a host of improved features, Holley's Ultra Series carburetors sport an external throttle shaft linkage, thus eliminating worry of loose parts finding their way into your intake manifold.
Along with that, the Ultra Series carburetors received billet metering blocks and base plates that are longer-lasting and eliminate porosity, glass fuel level sights for ensuring your float bowls have the proper amount of fuel inside, a new external throttle shaft linkage design, teflon-coated throttle shafts that improve airflow, hand-polished venturi inlets, and 12-hole billet booster inserts. Adding to the highlights of these refined carburetors is the weight savings, which is five pounds on the street models and four on the Dominator.
Advanced Engine Design was founded 28 years ago by John Dickey with one basic premise: to manufacture high quality components at competitive prices. And their more than two decades of involvement in the automotive aftermarket industry in designing, building, and research and development on high performance carburetors and fuel system components has elevated them among the markets’ elite.
AED Performance has gradually taken their existing carburetors castings and performed offset boring and other methods in order to outfit them with larger throttle plates. Said Dickey, “you’ve got guys building street motors that are 500, 600, 700 cubic inches and driving them on the street, and race teams are building engines bordering on 1,000 cubic inches. It’s pretty amazing.”
AED's Max-Pro Dominator is one of their largest carburetors with sizable throttle bores and billet, and is designed for big cubic inch race motors
Dickey points out that it’s quite difficult to size everything appropriately off of an existing casting, thus AED and others have had to get rather creative in building a carburetor large enough to supply today’s motors.
“The problem is that if you don’t have a carburetor that flows enough cfm, it’ll create an excessive level of manifold vacuum. Then it creates so much pumping loss that you’re giving up a whole lot of power. As manifold vacuum builds, the carburetors have a tendency to quit pulling air and use more fuel, and then they go really rich up top. So getting the fuel out of the top of the fuel curve by sizing things appropriately and bleeding off the circuits has been important. You just have to make things bigger.”
Like others, AED has also refined their billet booster design for use with alcohol over the course of the last six months. The grooves within the booster have been opened up to allow for more fuel, more holes, and more area behind it to contain more fuel for higher-powered applications.
As is standard these days, AED produced their metering blocks from billet aluminum material, delivering the ultimate in fuel curve tuning & adjustability.
“The problem in the past with an alcohol booster is that there’s so much mass of fuel – alcohol use 2.1 times the fuel – that it’s tough to get enough fuel in there so you can supply the motor and keep the curve flat up top. But they have a tendency to go lean. Now you can do this with alcohol, even on engines that makes a lot of power, and get it so that you don’t have a fuel lean-out condition up top.”
Another area of focus for Dickey and company has been the needles and seats. AED has implemented the use of an entirely new bottom feed needle valve, albeit with a similar shell, and whereas previous designs from AED and other manufacturers saw the needle valve function in a side-feed manner, the fuel now flows out of the bottom of the seat. Essentially, the needle and seat have been reshaped and enlarged into a ball shape that allows for fuel run beside it and out the bottom of the seat, which has helped to increase fuel flow by 23% through the same size hole.
The fuel flows through the main holes in the bottom of the body, and an additional set of holes in the lower part of the body allows for fuel enter through the the sides and the bottom so that all of the fuel isn’t trying to come out of one place in the bowl. This cuts down on phoning – or flooding – and adds more capacity.
Like all carburetor manufacturers, AED has continually looked for new ways to enlarge their carburetors to keep up with the massive size and power output of todays race engines. Their top of the line 4150 alcohol carburetor is the quickest and fastest unit they've ever produced.
“This becomes really important in high-flow situations where you need a lot of fuel; a single carburetor running big power levels with a blow-though application, for example. And we’ve also used it on other high horsepower combinations with single four-barrels and even in Pro Modifieds with dual carburetor setups.”
Also important for Dickey and AED has been the advancement of their carburetor designs for the growing number of blow-through turbocharger combinations, which present a number of differences from their naturally aspirated counterparts. These applications generally produce more horsepower and require more fuel, and with more than ten pounds of boost, the carburetor baseplates are pressurized to the point that fuel can actually be pushed by the throttle shafts into the engine. To rectify this, AED has machined and sealed the baseplates with o-rings; a measure that Dickey says can also be accomplished by machining a pressure channel in the baseplate and using the boost pressure to neutralize the pressure difference.
AED has also focused on the fuel curve needed for such applications – where the higher fuel demands effect the fuel circuity – by sizing the main circuit according to the boost and RPM levels from the main well, cross well, and booster opening. The power valve channels also have to be resized to try and supply additional fuel under boost. Along with that, booster selection and preparation has been key, as the carburetor experiences an entirely different dynamic when pressurized from the top rather than from the cylinder below.
“Blow-Through situations are much harder especially at elevated boost levels as this curve is not linear as fuel flow does not keep the linear pace with increased airflow. This is the key to life of these engines & requires a different approach than conventional carburetor preparation,” Dickey explains.
Dickey continues, “we are currently working on developing a whole new approach to rectify the situation instead of just trying to compromise with current technology. Like everything the more you know the more you realize how much is still to be learned to evolve the components to another level.“
Like Holley, many of Pro Systems’ recent contributions to the carburetor landscape have been incorporated into and revolve around a single carburetor design: the SV1.
Pro Systems, led by owner Patrick James, has been a part of the racing world for the last 15 years and with a sole focus on the highest of high performance carburetion and fuel system components, they’re certainly among the best at what they do. And they take deep pride in their innovative new SV1 unit.
The “SV” in SV1 stands for Single Venturi, which rather than sporting multiple barrels like all other designs on the market, the SV1 features a single inlet with special port layouts and impressively high cfm ratings that were previously unattainable with other designs.
Explained Patrick, “the one barrel has really been the best way to do a carburetor in the first place, it’s just that no one could figure out how to do the booster. With the previous two booster design, it just didn’t work. It didn’t have any low-speed signal.”
Pro Systems founder Patrick James formulated the working concept for his single venturi vision while troubleshooting a nuclear reactor. It was there that he learned how to make the entire booster on the SV1 produce boost, thus allowing for the superior single venturi design.
Patrick actually formulated the concept for his newest generation carburetor while working with Northrop Grumman on a nuclear reactor, where he helped to remedy unwanted turbulence they were experiencing within their water coolers.
“I figured out a way to stop the turbulent “flopping” issue by introducing air along the backside of the tubes in the water cooler, which reduced their pumping costs by some 30%. And then it hit me, that’s the biggest problem with the tube deal with the boosters and the reason why we could never use a tube; because it would flop left and right at low air speeds,” James said.
By using the fuel as a curtain, Pro Systems was able to stop the flopping and introduce the fuel out the bottom or the side rather than off the end. Armed with the revelation that the whole booster could be used a single generating device rather than just the end of it, the single venturi design became a reality. Because unlike a typical four barrel booster, the entire booster on the SV1 produces boost.
A design view of Pro Systems' SV1 carburetor, featuring an innovative single venturi throttle plate.
“With that, we were able to narrow down to a single venturi. Imagine if you were going to move oil through a pipeline: you wouldn’t use four small pipelines, you use one big one,” Patrick explained.
With current four barrel designs, when the throttle blade goes fully vertical, it’s dead center underneath the middle of the booster, thus blocking it. On the SV1, because the entire booster is generating signal, when vertical, all the holes for signal generation are on the opposite sides of the blade. Thus when wide open, air comes rushing in and fuel comes rushing right in with it, and where air/fuel ratio lean spikes commonly occur, the SV1 doesn’t exhibit. that equates to more torque right at the hit of the throttle and on the shift points.
And thanks to the improved booster design, whereas a four barrel commonly struggles to idle anywhere under 1,100 RPM, the SV1 idles as smoothly as an EFI system down to even 700 RPM. “The design, by physics, is the proper way to do a carburetor. It’s just a better way to do the job,” James claims.
Quick Fuel Technology
Quick Fuel says they were the first manufacturer to produce a 100% aluminum carburetor, including the main bodies, metering blocks, and bowls. Said Quick Fuels' Shane Montgomery claims, "the casting is more straightforward and it yields a better product.""
A relative newcomer to the industry, Quick Fuel was founded in 1998 and has grown by leaps and bounds since that time, making itself one of the benchmarks by which carburetors are measured. among their product lineup is the QFX, RaceQ, and Hot Rod Series carburetor lineup that cater to the racing and high performance world.
Quick Fuel claims to be the first in the industry to switch the main castings of their carburetor over to the lighter aluminum from the zinc material that had been the standard for much of history. Over the decades, zinc had been developed and refined to a very solid point in terms of machining, manufacturing, and casting, but as Quick Fuels’ Shane Montgomery argues, “there are always porosity and corrosion issues associated with zinc, whereas aluminum is more of a pure metal. The casting is more straightforward and it yields a better product.”
Quick Fuel claims they were the first to unveil CNC machined billet aluminum metering blocks that eliminate porosity and variance.
Quick Fuel’s argument is the aluminum construction, although still susceptible to some porosity, is a superior heat dissipator, lighter, and is more corrosion-resistant. With aluminum, one can simply polish it or perform a tumbled-finish without worry of anything attacking the finish any further. Plus, there is some weight savings.
Prior to their introduction of aluminum main castings, Quick Fuel says they first unveiled billet aluminum metering blocks to the industry. “The metering circuits in the metering block,” explains Montgomery, “are the most critical elements to your curve and the overall performance of the carburetor, and in being CNC machined from a solid block of aluminum, it has a much greater tolerance as far as the specification you’re going off of. There’s no variance, no porosity, no channels that misalign; it’s all just high-precision, exact machining.”
In addition to the metering blocks, Quick Fuel also produces aluminum throttle bodies and fuel bowls, making their carburetors 100% aluminum.
As aluminum components have become more the standard in the racing carburetor world, Quick Fuel has worked to incorporate tuning features to virtually every facet of the carburetor, thus making each element adjustable simply by changing out orifice bleeds. This has simplified the practice of tedious machining down to just replacing screw-in bleeds with another using a screwdriver. This not only makes tuning a much easier process, but allows for placement of the same carburetor on another engine with some adjustments.
“There’s a myriad of stuff going on in the carburetor world that the public probably doesn’t realize or pay much attention to, and they may not think it’s a big deal, but for something that’s been around and relatively unchanged since the mid-50’s, there’s all kinds of things happening each year that makes them better and better,” said Montgomery. “But if you’re a carburetor geek, they’re big steps and a big deal.”
As Quick Fuel’s Shane Montgomery stated and the other manufacturers that we spoke with echoed, despite the gradual changes seen on the surface, the fabled carburetor is far from dead and development is continually occurring behind the scenes to make every facet of high performance carburetors just that much better. And as electronic fuel injection has further gained traction in the high performance and racing world, the fire has only burned brighter for those making things happen in the carburetor market.
Said Dickey, “I’m still a believer that even with all of the injection systems out there, we can still make as much power with the carburetor in most cases, and in many cases, more power with the right manifold and carburetors than you can with injection.”
Mighty good news for the purists among us still near and dear to the traditional carburetor.