The fuel injectors used in high-horsepower drag racing applications aren’t just re-flowed OEM units–they are precise pieces designed to work with amazing accuracy. Selecting the correct injector for your engine is a process that requires expert insight to prevent catastrophic failures and performance issues. For the Pro Line Racing Hemi in Project BlownZ06, we added two sets of 700 pound-per-hour injectors from Atomizer Fuel Systems along with a full Aeromotive fuel system to keep the boosted engine full of fuel and making horsepower efficiently.
The simplest way to describe a fuel injector is that it’s a valve which opens and closes like a solenoid to provide fuel for the engine. When the injector is opened and closed by commands from the ECU, it is also being told how much fuel to send into the combustion chamber, and when to send it, based on the tables built by the vehicle tuner. The fuel system is also simple in theory: it consists of a pump and its associated filters, lines, and fittings, sized properly to ensure more-than-adequate fuel volume under heavy demand.
We enlisted the experts — Jack French from Atomizer Fuel Systems, Brett Clow from Aeromotive and Chris Jones from Pro Line Racing — to line out the details of what makes a fuel system perform properly in high-demand applications, how to ensure you’re selecting the proper injector and pump size for your application, and when more than one injector might be required.
What Goes Into A High-Performance Injector
French spent over 23 years in the automotive OEM design and manufacturing world before he started his company. He used the extensive experience and knowledge he gained during that time period to help develop his line of Billet Atomizer fuel injectors that are found in some of the most powerful racecars in the world today.
The biggest difference between an injector like the Billet Atomizer units and an OEM-style injector is the fact that the Billet Atomizer injector can be rebuilt. All of the injectors that Atomizer Fuel Systems produces are hand-built and made of billet aluminum rather than mold-injected plastic. The Atomizer injectors use a larger coil and faster-responding internal geometry which allows them to be infinitely more precise than a typical OEM-style fuel injector.
“Our Atomizer injectors are made from military-spec materials which are more expensive, but are much higher quality and heavy-duty. The materials are also much more magnetic in nature, so that allows them to be opened and closed more precisely when they’re activated. That precise activation leads to an injector that functions more consistently, even at higher RPM levels,” Jack states.
Since we are running BlownZ06 on VP Racing Fuels M1 methanol, getting the best fuel atomization is important due to how M1 reacts in the combustion process. An OEM-style injector will have five holes or less in the tip, where the Atomizer 700 lb-hr injectors we’re using in the Pro Line Hemi have 43 holes, and the injectors themselves are physically larger than the OEM-style injector. The Atomizer injectors use their faster opening and closing times to take advantage of this greater atomization ability.
Jack adds some additional detail as to how the holes help break up the fuel for proper atomization as it leaves the injector.
“It’s important in methanol applications that the fuel is really broken up as it is sprayed out of the injector. Methanol isn’t as volatile as gasoline, so you have to get the droplet size of the spray as small as possible to get a quick and complete burn. We spec the meth injectors out at a higher pressure rating to account for this, as well,” he explains.
Our Atomizer injectors are made from military-spec materials which are more expensive, but are much higher quality and heavy duty. – Jack French
If you sit an Atomizer injector side-by-side with an OEM injector, you will notice just how much larger the Atomizer injector is. This size difference in the outside of the injector actually plays a role in how it will perform internally. Fuel injectors operate using magnetic fields to open and close the internal parts of the injector quickly. That quick movement is what allows a high-end injector like the Billet Atomizer unit to move fuel at a high enough rate to keep up with a performance engine.
“The density of the material on the outside body of the injector plays a role in the eddy current dissipation, which is basically the release of the magnetic field. To get this current to function properly, the injector must be a certain size and have specific measurements for its materials. That’s why we have made our injectors the sizes they are and use higher quality materials in their construction,” Jack states.
As noted previously, one of the big bonuses of the Atomizer injectors is their ability to be totally rebuilt. Parts inside like the coil, internal components, and lower bodies can be rebuilt or replaced if there’s any type of failure. The injectors are also fully calibrated in-house within one-half-percent to make them as precise as possible. This enables Atomizer Fuel Systems to provide injectors which are matched to the engine application the end user has in mind.
Size Matters: Injector Sizing 101
Selecting the injector package for your new engine isn’t something that can be done with some guesswork; it requires specific information to be sure you’re feeding your engine the right amount of fuel. The general guidelines which should be used to help select a set of injectors must take into account the type of fuel you are using, the approximate target horsepower the engine will be making, and the type of power adder you’ll be using if that’s part of the combination.
Pro Line Racing uses Billet Atomizer injectors exclusively on any of their EFI builds, and shop manager Chris Jones talks about how they size them for each application.
“We use the standard guidelines that Billet Atomizer provides to us for all of our setups since we use their injectors exclusively here at PLR. These are mathematical calculations based on the power level, RPM, fuel type, and fuel system pressure. The Atomizers use slightly lower duty cycles than many other injectors to keep them cooler during operation,” Jones says.
Since BlownZ06 is using a ProCharger supercharger which is crank-driven, it requires more horsepower to spin the blower versus a set of turbos, and therefore you have to pump more fuel into the engine.
“Blowers tend to increase the air temperature charge and so forth, so when we size a blower injector, we take the calculation percentage of fuel and horsepower, then add a number to that because it’s a blower. In other words, the same turbo engine that makes similar horsepower takes less fuel than a comparable blower engine making the same power. I would size a blower application with more injector than a turbo application.”
OEM Injectors vs Billet Atomizer Injectors
Fuel injectors are basically made of an outside body, the pintle, internal guiding surfaces, and internal parts. The internal difference between an OEM injector and a Billet Atomizer injector is that the OEM injectors have permanent processes done to them like crimping and laser welding of parts. So if you wear out an internal guide or other parts you have to throw the OEM injector away, whereas the Atomizer injector can be serviced with replaceable parts.
“If you don’t have enough injector for an engine combination, it can really do some harm. You will see lean conditions and this comes from the overtaxing of the injectors on duty cycle leading to failures,” Jones states.
French agrees with Jones when it comes to the importance of the injector duty cycle and not going beyond what it can do.
“Duty cycle is a big factor in sizing your injector, just like fuel type and horsepower. I like to target the injector duty cycle of any application in the 70-percent range. So when you get into a high-RPM situation, say 10,000 rpm, you only have so much time to get the right amount of fuel in. When you only have about 12-milliseconds to get the fuel in the cylinder, the duty cycle has to be kept down to make sure the injector opens and closes accurately.”
The displacement of the engine and if a power adder is being used are important when injector size needs to be determined. Every engine is designed to make a certain amount of power at a given RPM level, and power adders assist in dictating what the engine’s final output will be.
“The size of the engine has more to do with where that power occurs in the rev-band. Believe it or not, the 481X and Hemi engines typically use the same injectors: twin Atomizer 700s, regardless of them being utilized in a low-boost, twin 88mm turbo setup like an NHRA Pro Mod, or an all-out RVW car with twin 106mm turbos. We always have more than enough fuel system capacity to keep the injectors fed with fuel. The tuners use fuel pressure, duty cycles, and pulse widths to manipulate them to work in every case. We are afforded this luxury due to the Atomizer injector technology,” Jones explains.
The fuel you are using is also a big part of the equation when you’re trying to get the correct injector for your combination. For BlownZ06, since we are running methanol and pushing a lot of horsepower, both of those factors had to be considered during the injector selection process.
If you don’t have enough injector for an engine combination, it can really do some harm. – Chris Jones
“When you’re using M1 for fuel, it’s really important to know the amount of horsepower you’re targeting because you have to make a non-linear calculation when choosing the injectors,” French explains. “The more power you start putting into an engine, the higher the brake specific fuel consumption (BSFC) goes because the intake air charge gets hotter and hotter, so it takes more fuel because the hot air starts to vaporize the fuel quicker. So basically what I like to do is size the injector based on the targeted horsepower and type of power adder and then do the calculator from there.”
For example, a 2,500 horsepower turbo car on M1 will take X amount of injector and at a BSFC of 1.9, as you get closer to 3,000 horsepower and up the BSFC goes up to 2.2 or more. This goes up because it’s non-linear. Since the air charge is heated, it takes more fuel to keep the engine happy,” French shares.
Single Injectors And Dual Injector Set Ups
Earlier in this article, we touched on what can happen if you don’t have enough injector capacity for your engine and the negative impact it will have. What do you do if your target horsepower exceeds the limits of a single injector? The answer is simple: You add another bank of injectors to feed your hungry engine.
“For the most part, the need to go to a twin injector setup is based on fueling requirements for the engine. If you have a single injector setup that’s right on the edge with pulse-width and duty cycle, and you can’t go up another size, the twin setup is the way to go. Most of our gasoline engines utilize single injectors to this day. A mixed setup like a Drag Week build can have a twin setup in some instances due to driving on pump fuel and racing on methanol. The cruising injectors will be fairly small and act as a piggyback to the larger injector when you go into race-mode and have more fuel consumption,” Jones says.
Jack prefers to use a single injector whenever possible because it limits the number of things that go wrong. If an injector driver fails, or a wire comes loose on a dual injector application, it will cause that cylinder to go lean, and that’s when you start hurting parts. The Atomizer 4 injector will be capable of moving enough fuel to be a single injector solution in the future, but in the meantime for big horsepower engines, the dual injector setup is the way to go.
The Pro Line Racing Hemi paired with a F3-136 ProCharger makes a lot of boost and power, so a set of dual 700-pound Billet Atomizer injectors had to be used. This setup allows for enough methanol to flow to support well over 3,000 horsepower and lay down three-second passes in Radial vs The World trim.
According to French, these types of numbers validate the need to have a dual injector setup on engines that make massive amounts of horsepower.
“At certain power levels, dual injectors are really needed to get the fuel in the motor. If you have more air than you have fuel, you’re either going to be limited on power or you will start destroying parts.”
Pumping The Fuel For BlownZ06 With Aeromotive
Feeding the VP Racing Fuels methanol to the Atomizer Fuel System injectors on BlownZ06 takes a super-stout fuel system. To make sure we had enough fuel flow, we enlisted the experts at Aeromotive to help us determine the proper course of attack with respect to fuel supply. After looking at all the options available to use on the Pro Line Hemi, one of Aeromotive’s 22 gallon-per-minute (GPM) Spur Gear Pumps was the best fit for such an extreme application like BlownZ06.
The Spur Gear pump from Aeromotive is extremely versatile with its plumbing options since it offers a variety of inlet and outlet attachments, along with different size distribution blocks. The pump has the ability to be mounted with three- and four-bolt flanges along with a V-band adapter. These pumps can flow anywhere from 16-32 GPM of fuel, whether its gas, alcohol, or even nitromethane.
According to Aeromotive’s Clow, the parts of the Spur Gear pump are what makes it so durable and the best choice for the BlownZ06 Corvette.
“The Spur Gear Pump is a modular line; what you have is a pump body with the same physical size body, but the gearset height is what determines the amount of fuel they flow. The tooth-count on the gears is the same, but as the gear gets taller it has the ability to move more fuel. We have specialized wear plates that go inside the end caps to set the tolerances for the gear set, so if you have a shorter gearset you will have a thicker wear plate.”
Aeromotive uses what they call a “pump-centric” approach when it comes to how they size the fuel system for an application. The job of the pump is to supply the correct amount of fuel to run the engine at its maximum potential; after a pump is selected everything else falls into place in the sizing process for Aeromotive.
Sizing a pump properly for a methanol application takes a bit more thought for Clow to ensure there are no issues when the engine roars to life and begins to make passes at the track.
“Methanol is the most challenging fuel to predict volume for because of how it’s used and the ways it can be introduced. Different applications, whether it’s a carburetor, turbo EFI, or blower will have a 40- to 50-percent variation of how it will burn the methanol based on how it’s making the power. I’ll add about 20-percent on the return line to make sure it flows enough and has a margin of error if we want to make more power.”
The pump size is based on the amount of predicted horsepower the engine will produce, the fuel it will run on, and how it will make power (nitrous, blower, turbo, etc.). After Aeromotive has this information, they can establish the gearset the Spur Gear Pump will need, and the best approach to plumb the pump into the fuel system.
How the pump is driven is the final factor that is examined in the process, according to Clow.
“Most of these spur gear pumps are hex-drive and are driven off the camshaft or the back of the oil pump. Some use an adapter to allow it to be belt-driven, as well, based on the application. They can also be driven off an auxiliary drive on the drive unit for the supercharger. The pump runs at 50-percent of the engine’s rpm, so you have to look at the flow curve on the pump. As the pump runs slower it flows less, and as it spins more rpm it flows more. The standard to base the pump flow is on 4,000 rpm, when you’re looking at the gallons-per-minute. You factor into the equation of sizing the pump and the rpm level the engine will be spun at so you know what flow curve will meet the fueling need. You might have to go to a larger pump to make sure the pump will flow enough at lower rpm in some cases to avoid fueling issues.”
The spur gear pumps we use are more forgiving when it comes to debris, there’s less surface area for fiction to be generated, and they cavitate less so are more efficient pumping at higher volume levels. – Brett Clow
Aeromotive has spent a lot of time developing the Spur Gear Pump, with the input of the top engine builders and racers in the world. These teams were making minor changes to enhance their pump’s flow and reduce cavitation at high speed. Aeromotive has brought that information and their feedback into the Spur Gear Pump design so there is no need to modify the pumps anymore.
Beyond the design improvements, the Spur Gear Pumps are a durable unit that’s a perfect fit for an application with big fueling needs like BlownZ06.
“The spur gear pumps we use are more forgiving when it comes to debris, there’s less surface area for friction to be generated, and they cavitate less so are more efficient pumping at higher volume levels,” Brett says.
Additional Fuel System Parts
Another part of the Aeromotive fuel system used on BlownZ06 is the 13132 Fuel Pressure Regulator. A high-horsepower, methanol-fueled, EFI application like BlownZ06 requires fuel pressure to be precisely controlled, to prevent any hiccups that could cause fuel starvation—and the subsequent destruction that could occur as a result of such.
According to Clow, having a regulator that can keep up is crucial to the fuel system working correctly in an EFI application.
“If you have to pedal the car or are free-revving the engine, if you don’t have a regulator that’s engineered to be efficient, that’s to say when there’s not a lot of fuel on the return line, it’s going to be able to effectively restrict what’s left and keep the pressure from falling. The regulator also needs to have the capability to bypass all the extra fuel without stacking fuel pressure, too.”
The final piece of the fuel system puzzle that Aeromotive put into place on BlownZ06 is the fuel filter. In the system, the filter’s role is to protect whatever is downstream from it while not being a choke point for the fuel itself.
“Having enough surface area on the element that can flow the volume without causing a flow restriction or pressure drop across the element is important. The filter and element are designed to work with all of these and be invisible to the system while still flowing the fuel amounts needed,” Clow explains.
It’s great to have the best parts possible for the BlownZ06 fuel system, but they’re worthless unless they’re all connected. To make sure we had the best flow possible for fuel and the rest of the vital fluids on BlownZ06 a full complement of Earl’s Performance Plumbing Ultra Pro Series hose ends and hose was used. This provided the build team with plenty of options for routing all of the fuel lines for the engine where they needed for ease of maintenance and peace of mind when it comes to performance.
Since BlownZ06 is a very extreme application for any performance part the choice of using the Ultra Pro Series made the most sense for the fittings. These fittings have the ability to be used in a variety of positions with the trick swivel technology that Earl’s has built in. These fittings are also resistant to most chemicals via the internal seals, which helps to prevent leaks under the hood. Each fitting is made from 2024 aluminum to provide the most strength possible without adding to much weight. Finally, a tough anodized coating is added to help the fittings look good and deal with the harsh conditions that can be produced under the hood of a racecar.
Transferring all the vital fluids for BlownZ06 is the polyester braid UltraPro hose from Earl’s. This hose features a PTFE inner liner that can handle any fluid and won’t be damaged by anything. The inner liner also has the ability to flow large amounts of fluid due to its low coefficient of friction, so this keeps the Corvette’s pumps from having to work harder than needed. A big advantage the UltraPro hose provides is that it’s 67-percent lighter than your standard rubber hose with a stainless steel braid. If you think about how much plumbing goes into a car like BlownZ06, that adds up quickly and the weight savings allows the team to add weight ballast where they need it more.
Selecting the correct fuel injector and fuel pump setup for a high-powered drag racing engine is crucial to making sure the full potential of the combination is reached. By considering all of the important factors like targeted horsepower, fuel type, and if a power adder is being used, choosing the right fuel system components becomes much easier. When you arm your engine with the right injectors and fuel pump, it will reward you with big power, lots of reliability, and remain easy to tune when you’re at the track.