Aeromotive Fuel Systems Insight - CHP Insider

Jesse Powell And Brett Clow Of Aeromotive Explain The Science Behind Fuel Delivery And How To Properly Design A Fuel System

Stephen Kim Jun 1, 2009 0 Comment(s)
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Sure, it's twisted, but with gas prices so low these days, our idea of going green is burning as much of the stuff as possible while it's still cheap. You can't get much greener than the color of cash, and it will pump money into the economy to boot. Accomplishing such an altruistic endeavor requires a serious fuel system, and Aeromotive has the goods to get the job done. Since opening for business in 1994, the company's pumps, filters, and regulators have been the choice of countless street/strip enthusiasts and hardcore racers. In fact, the fastest nitrous-powered car on the planet, Mike Castellana's IHRA Pro Mod F-body, relies on an Aeromotive fuel system while ripping down the track in six seconds flat at 239 mph.

That said, it takes a lot more than a brute pump to survive the rigors of racing and street driving. "If you want to do it correctly, getting the fuel from the tank and into the engine is far more involved than you might think," explains Aeromotive's president, Steve Matusek. "When Aeromotive was formed, our original goal was to design and manufacture the best fuel pumps, filters, and regulators on the market. Our philosophy has evolved over to years to one where we develop entire fuel systems, not just individual components. Engineering components to work together within the tolerance of one another results in seamless performance and maximum durability and reliability."

To educate us on the subject, Jesse Powell and Brett Clow-two of Aeromotive's head tech gurus-gave us a condensed dissertation on fluid transfer dynamics and fuel system design. Our heads are still numb from trying to translate it all into something that resembles everyday English, but we think the results were well worth the effort. Some of what we learned was downright shocking. Little did we know that mechanical pumps trump their electric counterparts, and that just about every carbureted fuel system can benefit from running a return line. Are you ready to get pumped?

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Calculating Flow Requirements
In the past, fuel pump manufacturers have rated their offerings based on gallons per hour of flow at an unspecified pressure, with no reference to test voltage. In the real world, this gave no indication of the horsepower that could be supported by their pumps. By choosing to assign a horsepower rating, along with publishing flow information at actual pressures and realistic voltages, Aeromotive has broken the mold and raised the bar for the industry. In the Aeromotive catalog, each pump carries several horsepower ratings on the basis of application type and use of power-adders.

The key variables that determine which fuel pump is suitable for a particular engine combination are horsepower, brake specific fuel consumption, maximum fuel system pressure, and the pump's flow volume at that pressure. Available voltage at the pump under engine load and the pump's flow volume at that voltage are important factors as well. To be safe, start by estimating horsepower on the high side and BSFC on the low side, which is usually less than one in most gasoline engines. Different engine combinations, power-adders, and even fuel octane ratings and tuning approaches will have a profound impact on BSFC, so consider this carefully when choosing a fuel pump.

Naturally aspirated engines are normally most efficient with a BSFC between 0.4 and 0.5 lb/hr. Nitrous combinations use a little extra fuel and often develop a BSFC from 0.5 to 0.6 lb/hr. Forced induction engines are usually the least efficient and have a BSFC ranging from 0.6 to 0.75 lb/hr. Determining the fuel volume necessary for a particular engine is the first step in selecting a fuel pump.-Brett Clow

Pressure And Volume
Designing a fuel system is a balancing act between pressure and volume. As system pressure goes up, the pump's volume goes down. "To illustrate this point, take a look at one of the most popular and efficient EFI pumps on the market, Aeromotive's A1000. Its flow volume is reduced 53 percent just by increasing line pressure from 9 to 90 psi," explains Powell. Although not quite as significant, he adds that the difference between 90 psi of line pressure and 60 psi with the same pump is a 28 percent drop in flow.

"A scenario like this isn't uncommon in forced induction EFI applications where fuel pressure is increased to compensate for undersized injectors. Clearly, the effect of raising fuel pressure has a significant impact on flow volume, and this is further compounded by low-quality fuel pumps. Obviously, eliminating unnecessary fuel pressure rise, removing FMUs, and installing properly sized injectors will increase flow and maximize the horsepower potential of any fuel system."

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Voltage And Flow
Voltage to an electric motor is like fuel pressure to an injector. More pressure in equals more volume out. Higher voltage at the pump terminals increases motor torque, resulting in more revolutions per minute and an increased flow volume for a given pressure. "Our A1000 pump will see a 40 percent increase in volume at 80 psi when voltage is increased from 12 to 13.5 V. This factor is often overlooked and can make or break pump performance, especially at high pressures," Powell explains. The key is to figure out how much a pump flows at a certain voltage. "Although often deleted on drag cars, the presence or lack of a correctly sized and properly functioning alternator is a vital consideration when choosing a fuel pump. Furthermore, proper wiring is no less important than proper plumbing when it comes to extracting the maximum performance from the fuel pump. Poorly executed wiring resists electrical flow to the motor, which manifests as a voltage drop at the fuel pump. In order to prevent this, we include high-quality wiring kits with our pumps along with detailed instructions."

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Feed Lines
After spending the time to select the appropriately sized fuel pump for the application, sizing out the feed line is rather straightforward. According to Aeromotive, the size of the line from the tank to the pump follows one simple rule of thumb: Don't make it smaller than the pump's inlet port size, and don't hesitate to make it bigger if you can. "This is easy to figure out with AN-style pump ports. For example, if the pump inlet port is AN -10, use AN -10 or larger fuel supply line, and make sure the tank outlet or pickup tube is the same size," says Powell. "When dealing with NPT threaded ports, use the line size that is a minimum of 1/8 inch larger than the NPT port thread. For instance, a 3/8-inch NPT port should have 1/2-inch (AN -8) lines. From the fuel pump to the engine, use a line size equal to the fuel pump outlet port for optimum results in low-pressure carbureted systems. This also applies to fuel-injected engines, although you can use a line that is one AN size smaller than the fuel pump outlet port and still get acceptable results."

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Return Lines
A common myth is that sizing the return line is based on the size of the feed line, but it has nothing to do with the size of the feed line. The lower the fuel system pressure, the larger the return line must be. Furthermore, greater fuel pump flow rates require a larger return line. A good rule of thumb is that the return line size must be large enough to handle the flow from the pump while creating at least 3 psi less backpressure than the regulator is set for.

The single biggest mistake we see is reducing the return port in the regulator to accommodate a smaller return line. This results in excessive fuel pressure regardless of how the regulator is adjusted. The solution is to treat the regulator return port exactly as you do the fuel pump inlet port. You can always make the return line bigger than the regulator return port, just like you can make the suction line bigger. This won't have a negative impact on pressure control. On the other hand, a restrictive return line causes excessive pressure, carb flooding, and drivability problems.-Jesse Powell

Venting
Although many people don't give it much thought, the consequences of improper fuel tank ventilation are severe. The tank vent should be equal to or greater than the size of the feed line to the fuel pump. This ensures that the fuel consumed by the engine is replaced with air, which enables fuel to flow smoothly out of the tank. Improper venting can result in a vacuum inside the cell, causing the pump to suck the fuel into a vapor. The results range from vaporlocking the fuel pump to poor drivability to catastrophic engine failure. "A good analogy is to think of the fuel system as a quart of oil," explains Powell. "As you pour the oil into the engine, it chugs in uneven spurts because there isn't enough air entering the bottle to replace the volume of oil that's exiting. If you were to poke a hole in the bottom of the bottle, however, oil would flow out smoothly."

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Beltdrive Benefits
The advantages of using a mechanical fuel pump over an electric pump in extremely high-horsepower applications are substantial. All electric fuel pumps exhibit a flow curve that declines with pressure, simply because the electric motor that turns the pump has a fixed amount of torque and consequently slows down as the fuel pressure, or work load, increases. Conversely, Aeromotive says that the loss in flow as pressure rises is virtually nonexistent with its G-Rotor mechanical pump design. "This is due in part to the pump's efficiency, but primarily because it's driven directly by the crankshaft," Powell explains. "In other words, there is no way engine rpm is going to be affected by the fuel pump. If an electric pump is equivalent to a 3hp, 12V electric motor, the current draw it would impart on a 1,500hp motor would be so extreme that it could slow its rate of acceleration. In all-out competition, a beltdriven pump is simply a superior setup."

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Deadhead VS. Return-Style Systems
Although most carbureted motors utilize deadhead-type fuel system, there is much potential for improvement in flow and pressure control by incorporating bypass regulators and return lines. This is particularly true with fuel pumps that don't have their own bypass capability. In the grand scheme of things, there isn't a single fuel system performance standard that doesn't improve when converting from a static (deadhead) to a dynamic (return-style) system. By running a bypass regulator, the pump can be set to run at lower pressure, thereby producing more flow, drawing less current, running quieter, and even lasting longer. Compared to a static setup, dynamic systems not only improve pump performance, but a bypass regulator also eliminates flow restrictions between the pump and the carburetor inlet. Plus, dynamic systems respond faster to fuel demand, and they do a better job keeping the float bowl full all the way down the track. In addition, dynamic systems never pressure-creep, which eliminates the engine flooding that static regulators can cause from time to time. The bottom line is that dynamic systems outperform static systems, and they simply produce the smoothest, most stable pressure curves. This has been proven in data logs from thousands of passes down dragstrips and laps around circle tracks.-Brett Clow

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Electric VS. Mechanical Pumps
Electric fuel pumps make up the vast majority of pumps produced and sold by Aeromotive. They're uniquely flexible, able to serve in both low- and high-horsepower applications, and work on the street, at the track, and in EFI or carbureted applications. Done right, they just flat-out work.

Over the years, racers and enthusiasts have historically moved from diaphragm-style mechanical pumps to high-performance electric pumps when they need more flow. Nonetheless, as horsepower levels climb, there's a point where we go from electric pumps back to mechanical. However, the mechanical pumps in question are belt- or direct-driven units that bear little resemblance to traditional diaphragm-style pumps.

In the early part of 2001, modern horsepower levels in EFI applications passed the 1,500 hp mark and were rapidly moving toward the 2,000hp barrier. Aeromotive founder Steve Matusek realized that electric fuel pumps had a practical horsepower limit, as dual electic pumps wouldn't suffice in certain applications. Recognizing this void, he created a G-Rotor based, engine-driven mechanical pump along with a matching regulator that enables fueling 4,000hp EFI motors. It has taken a number of years for people to catch on, but in that time many of the top racers in today's heads-up ranks have won with Aeromotive mechanical pumps, including Chuck Samuel, Doug Mangrum, Donnie Walsh, Steve Petty and Tim Lynch, David Shore, and Gary Rohe. Of course, our in-house six-second drag car runs our billet hex drive pump and regulator.-Jesse Powell

Filters
The bottom line is that a filter must flow what the pump is capable of flowing, essentially acting as if it's invisible to the pump. Accomplishing this requires optimizing porosity-or micron rating-and the filtering medium's surface area. Extensive testing has proven that any fuel filter with a micron rating less than 100 is too restrictive for the suction side of a fuel pump. On the flip side, fuel pumps are not nearly as sensitive on the pressure side. Consequently, micron ratings of 10 to 40 will suffice on the pump's outlet side.

Another key factor is the surface area of the filtration media. You'll notice that we offer several different filters, including several recommended for the suction side of our fuel pump. If you have ever spent any time on our site or with our catalog, you may have seen our Power Planner diagram, which is a systems-based recommendation of properly matched fuel system components for many different applications. In each systems, we have very specific filters that we match to different fuel pumps. Some of our larger fuel pumps require a larger filter than others. We know this because we have spent an enormous amount of time testing our fuel pumps. By making very specific parts-matching recommendations, we can ensure that our fuel pumps will operate in their ideal scenarios, increasing their durability and performance.

Furthermore, maintaining filters is critical to the life of your fuel system. After installing a new system, the elements should be cleaned or replaced after the first 5-10 run hours. The dirtiest a system will ever be is before it's installed. It's also important to note that paper elements must be replaced, but the stainless steel elements can be reused after cleaning. We recommend servicing your filters at least once a year after the initial service.-Brett Clow

Stealth System
The ideal location for a fuel pump is right inside the fuel tank, which is why the OEs have been doing this for quite some time. Mounting a big, electric external fuel pump inside a tank is extremely difficult, but the people at Rick's Hot Rod Shop have been doing it for several years now. "With their help, we developed a baffling system that surrounds the fuel pump inside the tank and maintains fuel at the point of pickup at all times. The baffling also controls fuel slosh as the fuel level decreases in the tank. In an ideal world, all pumps would be submersed in every application, so we set out to develop a way that will allow everyone to do so with our Stealth system," says Powell. The heart of the setup is a sump box that can be welded onto almost any fuel tank and that features an Aeromotive A1000 or Eliminator fuel pump and prefilter built right into the assembly. "When you weld this sump box onto the bottom of your fuel tank, you now have an in-tank fuel system that is properly sumped, baffled, and capable of supporting in excess of 1,000 hp. In addition to simplicity, ease of installation, and a streamlined appearance, the Stealth setup runs cooler and provides insulation from operating noise. It also features a return port that returns the fuel right back into the sump and offers easily accessible internals for maintenance."

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Pump Location
An external fuel pump, either electric or mechanical, should ideally be placed low and close to the tank. "Even if the pump is an Aeromotive A1000, which can pull like a freight train, you want to minimize the vacuum the pump has to create in order to draw fuel from the tank," Powell explains. "This avoids premature fuel vaporization and extends the fuel pump's duty cycle and ability to supply liquid fuel as fuel temperature elevates on hot days. This is very important because a liquid's boiling point drops as vacuum is applied on it. Airflow over the pump is not a bad thing, but will rarely solve other inherent design problems."

Vapor Lock
Aeromotive fuel pumps are extremely efficient by design, allowing them to create high pressure on the outlet and high vacuum on the inlet side. Cavitation to a pump is like detonation is to an engine and occurs when the liquid being pulled into the pump reaches a temperature where it boils and becomes vapor. A highly efficient pump matched with restrictive filters and feed lines can drop inlet pressure so low that fuel will vaporize unnecessarily at normal operating temperatures.

Fortunately, eliminating vaporlock is as easy as eliminating the causes. Proper line size is critical, especially on the suction side of the fuel pump, and filters must be up to the task as well. We recommend that 100-micron stainless steel filter elements be used on the suction side of the fuel pump. Many filters on the market today may say "100 micron" like we recommend, but what isn't mentioned is the filtration area. Our smaller filters have over 63 square inches of filtration media, ensuring there is ample room for flow, which eliminates the chance of pressure drop. We've seen numerous fuel pumps ruined by vaporlock because fuel filters with inadequate filtration surface area restricted fuel flow. Always look at the micron rating and the filtration area, as both are equally important to the life of your fuel pump.-Brett Clow

More Pumps & Tanks
Aeromotive will be releasing two new big-horsepower fuel pumps this summer, one for carbureted drag race applications and the other for EFI engines such as in Pro Mod. Additionally, the company will also be introducing its next generation of Stealth systems in the months ahead. "These will be fuel cells complete with an A1000 or Eliminator fuel pump and a prefilter already built in. Simply bolt the fuel cell in, hook up your fuel line and two wires, and you're ready to rock," says Powell. Cell size will range from 15 to 20 gallons. "We anticipate that these will be a big hit in the street performance and street rod markets since they greatly simplify the installation and eliminate all of the guesswork. You don't have to have a custom tank built and deal with the space issues for an externally mounted sump anymore. It doesn't get any easier."

Fuel Logs
A billet adjustable fuel log is a slick way to feed your carburetor, but many drag racers have shied away from them in the past due to sloppy clearances and poor fitment. Telescoping logs help alleviate some fitment issues since they have some flexibility and enable one log to fit several carburetors that share the same float-bowl-style inlets. Aeromotive took this concept a step further by not only making its fuel log a telescoping design, but also adding a ball-and-socket joint to each of the carburetor inlets that swivel 20 degrees in any direction. "This allows them to clear throttle stops, nitrous plates, and any other components around the carb," says Jesse.

"We have also added some other features not that common with a setup like this. Our swivel fittings allow attaching a bypass-style regulator right to the end of the log and rotating it a full 360 degrees while maintaining a positive O-ring seal. That means you don't have to mount your regulator on the firewall and run unnecessary fuel lines. We even offer kits that come with the fuel log, regulator, and swivel fitting all in one convenient package."

Sources

Aeromotive
Lenexa, KS 66214
913-647-7300
http://www.aeromotiveinc.com
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