Sylvie Willis
Selecting the right fuel injector size is crucial for engine performance and tuning control. The injector size depends on several factors, including the desired horsepower, engine type, fuel type, and injection system. For example, let's consider a 450 horsepower engine. According to some sources, a 28#/hr flow rate is the minimum required for 450 flywheel horsepower. However, others suggest that 22lb injectors may be sufficient, while larger injectors, such as 750cc or 1000cc, are also recommended by experts. It is important to note that factors like brake-specific fuel consumption (BSFC), fuel pressure, and engine specifications can influence the optimal injector size. Ultimately, tools like the FuelTech Fuel Injector Calculator can assist in determining the precise injector sizing needed to achieve the desired horsepower.
| Characteristics | Values |
|---|---|
| Minimum injector flow rate | 28#/hr |
| Fuel injector size | 750cc or 1000cc |
| Fuel pressure | 50-70psi |
| Fuel pump | Holley Dominator 12-1200 |
| Fuel injector connectors | Conventional, Peak & Hold |
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What You'll Learn
- Fuel injector sizing is critical for performance and tuning control
- The injector size depends on the engine's Brake Specific Fuel Consumption (BSFC)
- A higher BSFC may require a larger injector
- The injector's height and electrical connector should also be considered
- Low impedance injectors allow for smaller on-times
Fuel injector sizing is critical for performance and tuning control
The process of determining the appropriate injector size involves considering several factors, such as the engine's horsepower, the type of fuel used, and the number of injectors. By using tools like the FuelTech Fuel Injector Calculator, users can input relevant parameters to receive recommendations for fuel injector sizing. This helps ensure that the injectors can deliver the required amount of fuel to achieve the desired horsepower.
For example, let's consider a 450 hp engine. Using the formula horsepower x BSFC (Brake Specific Fuel Consumption), we can estimate the required fuel flow rate. With a conventional BSFC value of 0.50, the calculation yields 225 lbs/hr of fuel needed to achieve 450 hp. Dividing this by the number of injectors provides the desired fuel flow rate per injector.
However, it's important to remember that simply increasing the injector size does not always lead to better performance. Larger injectors can operate in a nonlinear zone at idle and light throttle, impacting drivability. Additionally, factors like the injector's internal components and spray pattern and fuel pump capacity also play a role in overall performance.
To ensure optimal tuning control, accurate injector data is crucial. This data allows tuners to properly control the fuel injector, especially during idle and light throttle driving situations. By choosing reputable injector manufacturers that provide detailed injector specifications, users can make more informed decisions when selecting fuel injectors for their specific applications.
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The injector size depends on the engine's Brake Specific Fuel Consumption (BSFC)
The conventional BSFC number for a gasoline engine is 0.50, indicating that the engine burns half a pound of gasoline per hour to generate one horsepower. However, due to advancements in engine combustion efficiency and reduced friction, this number can often be lower, dropping to 0.45 or less. To calculate the required fuel for a 450 hp engine, you can use the formula horsepower x BSFC, which, in this case, would be 450 hp x 0.50 = 225 lbs/hr.
It is important to note that the number of injectors also comes into play. For example, for a V8 engine with eight injectors, the lbs/hr necessary to feed the engine would be divided by eight, impacting the required injector size. Additionally, the injector size should be larger than the calculated value to accommodate potential increases in power without requiring a significant fuel pressure adjustment.
The BSFC value varies with engine speed and load, and different engine designs, compression ratios, and power ratings will result in different BSFC values. It is also worth noting that the BSFC is dependent on the type of fuel used, with some fuels, like E85, requiring larger injectors due to their higher BSFC numbers. Therefore, when determining injector size, it is crucial to consider not only the engine's horsepower and BSFC but also the number of injectors, the fuel type, and the anticipated power demands.
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A higher BSFC may require a larger injector
A larger injector is often required for boosted engines, especially belt-driven supercharged engines, as they consume a significant amount of crankshaft power to drive the supercharger. The larger the supercharger, the more horsepower it takes to spin the blower under boost. This additional power required to drive the blower must be accounted for when calculating the size of the injector necessary to make the boosted power. This can be done by changing the BSFC curve.
The BSFC, or Brake Specific Fuel Consumption, represents the amount of fuel an engine will require to produce one horsepower in one hour, expressed in pounds of fuel per horsepower-hour (lb/hp/hr). The conventional BSFC number for a gasoline engine has been 0.50, meaning the engine would burn half a pound of gasoline per hour to make one horsepower. However, with improved engine combustion efficiency and reduced friction, this number often drops to 0.45 or lower.
For a supercharged engine, the BSFC number will be higher, typically around 0.65 for gasoline, representing a roughly 33% increase in the amount of fuel required compared to a normally aspirated engine. This higher BSFC number for supercharged engines means that a larger injector may be required to achieve the desired horsepower.
For example, let's consider a 900 horsepower boosted engine with a supercharger making 15 psi of boost. The injectors must work against this increased pressure in the intake manifold, which effectively reduces the fuel pressure in the fuel rail. In this case, a larger injector would be beneficial to ensure sufficient fuel flow and prevent running a too-lean air-fuel ratio, which can have disastrous consequences.
It is important to note that sizing the injectors larger also provides advantages in terms of safety margins and accommodating future power upgrades. By sizing the injectors 20-30% larger, you can anticipate adding more power without requiring a significant increase in fuel pressure. This approach ensures that the injectors are adequately sized and can handle the demands of a boosted engine, preventing potential performance issues and engine damage.
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The injector's height and electrical connector should also be considered
When selecting a fuel injector, it is important to consider not only the required horsepower but also the injector's height and electrical connector.
The height of the injector is a critical specification, especially when dealing with limited space in the engine compartment. For example, the first-generation LS1 injector is much slimmer and slightly shorter than the older Bosch injectors, making it a more suitable option for passenger car applications.
Additionally, the electrical connector type of the injector is a crucial factor. There are multiple names for each connector, which can make the selection process confusing. For instance, the Bosch name for its early fuel injection system connector is "Jetronic," which later evolved into the Minitimer and then the EV1. The Delphi Multec 2 injector connector, for example, was used on most GM and Saab vehicles from 2001 to 2007, while the Nissan Z1 injector connector was used on several Nissan/Datsun Zcar models from 1990 to 1995.
It is also worth noting that the electrical connector can be damaged or broken over time due to various factors such as exposure to extreme temperatures or chemicals. Therefore, it is important to inspect and, if necessary, replace the electrical connectors to ensure proper function.
When sizing injectors, it is recommended to size them 20 to 30 percent larger than the calculated requirement to accommodate future power additions without requiring a significant increase in fuel pressure. This consideration also applies to the fuel pump, which must be capable of delivering the required volume and pressure of fuel to the injectors.
In summary, while determining the necessary fuel injector size for 450 hp is important, it is equally crucial to consider the injector's height and electrical connector compatibility with the specific vehicle make and model, as well as potential future performance enhancements.
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Low impedance injectors allow for smaller on-times
Low impedance injectors, also known as peak-and-hold drivers, involve high-pressure fuel pressure and large injectors, allowing more current to flow across the injector with maximum consistency. The circuit driver can regulate the current from 4 to 10 amps to open the injector. Once the injector is open, the current flow is decreased to keep the injector open. This type of design opens and closes quickly but gets hotter in a short time.
Low impedance injectors require a peak-and-hold injector driver, which allows for a higher opening current and then drops to maintain a lower current after the injector is open. This makes it easier for the injector to operate, especially with high fuel pressures. The peak-and-hold current can reach up to 56 amps to open the injector, and then the electrical signal can reduce to 23 amps to keep it open.
The major downside of low impedance injectors is their high cost. They are also known to increase the temperature of the transistor driver IC due to the increase in current flow, which can damage the driver transistor if the temperature remains high for a long duration.
Low impedance injectors are better for high-performance applications where a large amount of fuel is needed. They are typically used in purpose-built applications and are well-suited for high-flow, high-performance applications as they can deliver more fuel more reliably than comparable high impedance injectors.
In summary, low impedance injectors allow for smaller on-times by requiring a high initial current to quickly open the injector, followed by a lower current to keep it open. This two-step process enables faster opening and closing times, making them ideal for high-performance applications.
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Frequently asked questions
A 28#/hr flow rate is the minimum flow for 450 flywheel horsepower. A 750cc injector should be sufficient, but a 1000cc injector will provide extra fuel for more boost.
FuelTech offers engine management systems capable of controlling any fuel injector sizing. The FT600, FT550, FT550LITE, and FT450 are all-inclusive ECUs that feature sequential injection and ignition, O2 closed loop, Data Logger, Delay Box, Boost Controller, and Nitrous Controller.
It is critical to include the fuel pump needed to feed the injectors at the appropriate fuel pressure. The height of the injector along with its electrical connector should also be considered.
