Sylvie Willis
Fuel injectors are devices that deliver fuel to a vehicle's engine, and they are rated according to the amount of fuel they can deliver per hour, measured in pounds or grams. The fuel pressure, measured in psi (pounds per square inch), is critical to the performance of the injectors, with higher pressure increasing the flow rate and lower pressure reducing it. For Ford 42lb injectors, the fuel pressure is typically specified at 43 psi, but this can be increased to 58 psi to achieve a higher flow rate of around 48 lbs/hr.
| Characteristics | Values |
|---|---|
| Flow Rate in LB per hour | 42 LBS/HR |
| Flow Rate in CC per minute | 440 CC/min |
| Resistance | 12 ohms |
| Voltage | 8-15 Volts, nominal 13.5 Volts |
| Amperage | 1.0 Amps |
| Pressure | Min 30 PSIG/ Max 100 PSIG |
| Fuel Pressure | 43 psi |
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What You'll Learn
Fuel pressure directly impacts fuel flow
In a typical scenario, a 900-horsepower supercharged engine with a supercharger generating 15 psi of boost may have its fuel pressure in the fuel rail reduced from 43 psi to 28 psi. To compensate, a fuel pressure regulator is employed to detect the pressure in the intake manifold and adjust the fuel pressure accordingly, resulting in a rail fuel pressure of 58 psi and a differential pressure of 43 psi at the injector outlet.
The size of the injector also plays a role in fuel flow. For boosted engines, larger injectors are often preferred as they need to open against higher pressures compared to normally aspirated engines. For instance, a 900-horsepower engine with a supercharger producing 15 psi of boost will require injectors that can counter the pressure in the intake manifold.
It is worth noting that there are limitations to increasing fuel pressure. One of the main constraints is the fuel pump's capacity. For instance, to achieve a target of 1,000 horsepower, a 105 lb/hr injector would typically be required. However, a tuner might opt to increase the fuel pressure from 43 psi to 58 psi, resulting in a 15% increase in flow. Nevertheless, this approach assumes that the fuel delivery system can handle the increased pressure and deliver the required amount of fuel.
In summary, fuel pressure and injector size are critical factors in achieving the desired fuel flow. While increasing fuel pressure can enhance flow rate, it is important to consider the limitations of the fuel delivery system and ensure that the fuel pump has sufficient capacity to meet the demands of the injectors.
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Fuel pump capacity limitations
Fuel pump capacity is an important consideration when modifying your engine. The essential purpose of a fuel pump is to deliver fuel from the tank to the engine, and a high-flow fuel pump allows for a greater amount of fuel to flow to the engine. This flow is measured in gallons per hour (gph) or litres per hour (lph).
When upgrading your fuel pump, it is important to consider the type of fuel you plan to use. Some high-flow fuel pumps are rated only for use with gasoline and will fail if used with alcohol-based fuels like methanol or ethanol. There are, however, E85 ethanol- and methanol-compatible fuel pumps available.
It is also important to consider the other parts of your engine when upgrading your fuel pump. For example, too-small fuel lines or injectors can bottleneck the additional flow from a high-flow pump and negate the benefits. Additionally, fuel pump calculators can be used to determine the appropriate pump for your engine, but these can vary in their results.
The relationship between fuel pump capacity and fuel pressure is an important consideration. Fuel pressure has a direct impact on fuel flow, with lower pressure reducing the flow rate and higher pressure increasing it. This relationship can be determined using a simple formula. For example, an increase in fuel pressure from 43 psi to 58 psi results in an increase in flow of 15%. However, this also raises the base fuel pressure, and if the fuel delivery system cannot minimise restrictions, it may not be able to deliver the required fuel at the higher pressure.
In summary, when upgrading your fuel pump, it is important to consider the fuel pump capacity in relation to the other parts of your engine, the type of fuel you will be using, and the impact of fuel pressure on fuel flow.
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Higher fuel pressure increases flow rate
Fuel pressure is a critical factor in a fuel injection system. A change of just 1 to 3 PSI in fuel pressure can cause noticeable differences in engine performance. For example, a Ford fuel system may maintain an effective fuel pressure of 3 bar, or 36 PSI, but ramp up the fuel pressure to 88 PSI in the rail when there is increased demand.
Holley injectors are rated at 43 PSI unless otherwise specified. This is significant because fuel pressure directly impacts fuel flow. Lower pressure will reduce the flow rate, while higher pressure will increase it. For example, increasing the fuel pressure from 43 PSI to 58 PSI will increase the flow rate of 42 lb/hr injectors to around 48 lb/hr.
However, increasing fuel pressure is not the only way to increase flow rate. For example, increasing the duty cycle of the injector will allow more fuel to reach the engine. This is because the duty cycle refers to the amount of time the injector is open, so increasing the duty cycle will allow a greater volume of fuel to pass through.
Additionally, sizing the injector larger than necessary can offer advantages. For boosted engines with the injector located in the intake manifold, the injectors must open against higher pressures than with a normally aspirated engine. Therefore, increasing the size of the injector can compensate for this higher pressure.
It is important to note that there are limits to increasing fuel pressure. As fuel pressure increases, so too does the demand on the fuel pump. A high-quality, high-flow fuel pump is required to produce the necessary amount of fuel at the higher pressure. The entire fuel delivery system must also be capable of minimizing restrictions to deliver this fuel.
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Fuel pressure regulators are needed for boosted applications
Fuel pressure regulators are an essential component of any boosted application. They ensure that the engine receives the correct amount of fuel pressure, which is crucial for optimal performance. In boosted applications, fuel pressure can be significantly higher than in naturally aspirated engines, and it rises with boost pressure. This is why a fuel pressure regulator is needed – to increase fuel pressure under boost conditions and overcome the resistance created by boost pressure.
The basic function of a fuel pressure regulator is to maintain constant pressure by bleeding off any excess fuel. When boost pressure is low or a vacuum is present, the valve in the regulator is open, and excess fuel returns to the tank through the regulator's bottom port. However, when higher base pressure is set, the incoming fuel volume needs to work harder to push upward on the diaphragm and begin the return to the tank. This is where the boost reference line comes into play.
The boost reference line pressurizes the diaphragm housing of the regulator, making it more difficult for fuel line pressure to move it upward. This, in turn, allows for more fuel pressure, as the diaphragm spring assists the fuel line pressure. In boosted applications, the fuel pressure increases 1:1 with boost pressure. So, for every pound of boost pressure increase, the fuel pressure also increases by one pound. This ensures that the float chambers remain properly filled and that there is no interruption in fuel flow to the engine.
When selecting a fuel pressure regulator for a boosted application, it is important to consider the horsepower and fuel pump capacity. The regulator should be able to sense the pressure in the intake manifold and boost match the fuel pressure. Additionally, the regulator should be compatible with the fuel pump being used and have the appropriate number of ports to support the horsepower.
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Injector sizing impacts performance
Injector sizing has a direct impact on engine performance. Selecting the right size is critical for performance and ease of tuning in a fuel-injected engine. Bigger is not always better when it comes to injector sizing.
The size of the injector will determine the fuel flow rate, which in turn impacts the power and efficiency of the engine. Fuel pressure is directly impacted by the size of the injector. A larger injector will increase the flow rate, while a smaller injector will reduce it. This is why most injectors are rated at 43 psi—to ensure optimal fuel flow. However, it's important to note that this rating can be adjusted higher or lower depending on the specific requirements of the engine and the desired performance outcome.
For example, let's consider an engine with 42 lb/hr injectors rated at 43 psi. If we increase the fuel pressure to 58 psi, the flow rate will increase, and the injector will be able to deliver a higher fuel volume. This is particularly important for boosted engines, where the injector is located in the intake manifold and forced to open against higher pressures. In this case, a larger injector size can help compensate for the higher pressure and ensure the injector can deliver the required fuel volume.
On the other hand, there are limitations to increasing injector size. The fuel pump capacity becomes a critical factor, as a larger injector will demand more fuel at a higher pressure. If the fuel pump cannot keep up with the demand, the injector will not perform optimally. Therefore, when sizing injectors, it is crucial to consider the fuel pump's capacity to deliver the required volume of fuel at the appropriate pressure.
Additionally, the impedance of the injector plays a role in sizing. High impedance injectors are more common for street applications, as they have lower heat buildup and can run for extended periods with excellent reliability. Low impedance injectors, on the other hand, require a peak-and-hold injector driver, which is typically more expensive and used in aftermarket ECUs.
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Frequently asked questions
The fuel PSI for Ford 42lb injectors is 43.5.
The flow rate in CC per minute for Ford 42lb injectors is 440 CC/min.
The voltage for Ford 42lb injectors is 8-15 Volts, nominally 13.5 Volts.
