Regan Brown
Choosing the right fuel injector for your engine can be a challenging task. There are many factors to consider, such as the horsepower goal, fuel type, and plug type. The size and flow rate of the injector are also important considerations. Fuel injectors come in various plug types, with some being more common in older or newer models, and others being more common in imported vehicles. Determining the impedance of the injector is crucial, as it depends on the compatibility of your ECU. Additionally, the dead time, or lag, of the injector can impact the engine's performance, especially at low pulse widths. Proper sizing of the injector is critical for performance, and it's important to consider the fuel pump needed to feed the injectors appropriately. There are online calculators available to help determine the right fuel injector size, which is influenced by factors such as horsepower, fuel type, and induction type.
| Characteristics | Values |
|---|---|
| Horsepower goal | 500 |
| Fuel type | Gasoline, Ethanol, Race gasses, Fuel additives |
| Plug type | Ev1/Jetronic, Ev6/USCAR, Denso/Sumitomo |
| Impedance | High or low |
| Dead time | Time it takes the pintle to open and fuel to flow |
| Injector size | 32 lb/hr |
| Injector duty cycle | 70% |
| Injector flow rate | 330 cc @ 40 psi |
| Fuel pressure | 43 psi |
| Fuel injector size calculator | FuelTech, WitchHunter Performance |
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What You'll Learn
Fuel injector sizing
Horsepower Goal
Firstly, you need to estimate a realistic and accurate horsepower goal. This will depend on the specific engine you are using. For example, a Chevy truck engine from the "LS" family may have a horsepower goal of 475WHP.
Fuel Type
The type of fuel you plan to use will impact the size of the fuel injector you need. Different fuels have varying demands on the injector. For example, E85 fuel requires a roughly 30% higher BSFC number, meaning you will need a larger injector. Common fuel types include gasoline, ethanol, and race gases.
Plug Type
Fuel injectors come in various plug types, with some styles being more prominent than others. The most common types are:
- Ev1 / Jetronic: Found on earlier models, especially common on older low impedance injectors. They lack an internal O-ring and are not water-resistant.
- Ev6 / USCAR: More modern and common on new injector models. They feature an O-ring on the male end of the plug, providing water resistance and aiding in corrosion resistance.
- Denso/Sumitomo: Similar to USCAR, these are mostly found on imported vehicles.
Impedance
Whether you need high or low impedance injectors depends on the ECU you are running. Most ECUs are compatible with either high or low impedance. To determine the impedance of your injector, you can use an ohm meter across the injector's plug terminals. A reading of 1-4 ohms indicates a low impedance injector, while 8-16 ohms indicates a high impedance injector. High impedance injectors are generally preferred due to their lower electrical requirements, resulting in a cooler and more reliable electrical system.
Duty Cycle
The duty cycle refers to the percentage of time the injector is active during the engine cycle. For boosted engines, it is recommended to use a 70% duty cycle as a safety margin. For example, an 85% duty cycle is the maximum that should be seen on an ECU duty cycle display at max power.
BSFC (Brake Specific Fuel Consumption)
BSFC is another important factor in determining fuel injector size. It represents the amount of fuel required to produce a certain amount of power. By multiplying your horsepower goal by the BSFC, you can estimate the total fuel flow needed. For example, with a BSFC of 0.65 and a horsepower goal of 900, the calculation would be 900 x 0.65 = 585.
Number of Injectors
The number of injectors in your engine will impact the sizing. For example, a V8 engine typically has eight fuel injectors. You would divide the total fuel flow by the number of injectors to determine the size needed for each injector.
It is important to note that injector sizing is not an exact science, and there are many variables at play. It is generally recommended to size injectors 20-30% larger than your calculated needs to accommodate potential variations and future power additions.
To simplify the process, FuelTech offers a Fuel Injector Calculator that can assist in selecting the proper fuel injector sizing based on horsepower, fuel type, and other parameters.
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Fuel type
For example, let's consider ethanol, which has higher fuel flow requirements compared to gasoline. Ethanol requires approximately 30-40% higher fuel flow capacity to achieve the same air-fuel ratio (AFR) level as gasoline. This means that when using ethanol, you will need injectors with higher flow rates to compensate for its lower energy density relative to gasoline.
The specific type of ethanol can also make a difference. For instance, E85, a common variety of ethanol, will require a higher flow rate than standard ethanol. Additionally, the boost and cylinder head flow rate can impact the injector size and fuel flow requirements. It's important to note that higher boost and higher-flowing cylinder heads will increase brake-specific fuel consumption (BSFC).
Another factor to consider is the engine's horsepower, which is directly related to the amount of fuel it needs. Higher horsepower engines require larger injectors to deliver the necessary fuel volume. A good rule of thumb is that for every 1 horsepower (hp), you will need about 0.5 pounds per hour (lb/hr) of fuel. However, this can vary depending on the fuel being used and other engine specifications.
In summary, when selecting a fuel injector, it's crucial to consider the fuel type and its unique characteristics. Factors such as fuel flow requirements, energy density, and horsepower will influence the size and flow rate of the injector needed for optimal performance. By taking these factors into account, you can ensure that your engine receives the proper amount of fuel for efficient combustion and power production.
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Plug type
Fuel injector plugs are an important component of a vehicle's fuel delivery system, ensuring that fuel is injected with precision into the combustion chamber. The type of plug chosen must be compatible with the vehicle's make, model, and year.
There are several types of fuel injector plugs, each with its own advantages and disadvantages. For instance, some plugs are widely compatible with older vehicles, while others are more suitable for modern vehicles due to their enhanced design and better sealing. It's worth noting that some plugs may require adapters for compatibility with older systems.
One of the most common types of fuel injector plugs is the Jetronic/Minitimer connector. This type of connector is typically found on older EV1 fuel injectors. Bosch, a well-known manufacturer, offers fuel injectors with various injector connector/plug types, including the Jetronic/Minitimer (rectangle-shaped), USCAR (rounded-edge square-shaped), and OEM manufacturer-specific designs.
Another factor to consider when choosing a fuel injector plug is durability. Select plugs that can withstand heat, moisture, and vibrations to ensure optimal performance. Additionally, the plug chosen should support the vehicle's fuel delivery requirements while maintaining the necessary corrosion resistance, especially if the vehicle is used for racing.
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Impedance
Fuel injectors are categorized into two main types: high and low impedance. The impedance of a fuel injector is an important factor in determining the compatibility of the injector with the vehicle's Engine Control Unit (ECU). The ECU is responsible for controlling the injectors, and it is designed to work with either high or low impedance injectors.
High impedance injectors are the most common type used in street applications. They have a resistance value of around 12 ohms, resulting in a continuous current draw of approximately 1 amp. This design reduces heat buildup, allowing high impedance injectors to operate for extended periods with excellent reliability. High impedance injectors are typically driven by a saturated injector driver, which provides a continuous current to the injector.
On the other hand, low impedance injectors are less common and are usually found in aftermarket ECUs. They require a peak-and-hold injector driver, which initially provides a high current to open the injector and then drops to a lower current to keep it open. This type of driver is more expensive and is typically used in high-performance applications.
The impedance of a fuel injector can be measured using an ohm meter across the injector's plug terminals. If the meter reads between 1-4 ohms, it is a low impedance injector, while a reading of 8-16 ohms indicates a high impedance injector.
It is important to note that the choice between high and low impedance injectors depends on the vehicle's ECU compatibility and the specific application requirements. High impedance injectors are generally preferred due to their lower electrical requirements, resulting in a cooler electrical system and potentially increased reliability. However, low impedance injectors offer higher flow rates, making them suitable for high-performance applications.
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Fuel pump
Fuel injectors are an essential component of an engine's fuel system, delivering fuel to the engine to generate horsepower. The size and flow rate of the fuel injector are critical factors in engine performance and efficiency. To ensure optimal performance, it is crucial to select the appropriate fuel injector size, which can be determined using fuel injector calculators or by considering factors such as horsepower goals, fuel type, and plug type.
One key consideration when choosing a fuel injector is the horsepower goal of the engine. The injector must be capable of delivering enough fuel to meet the horsepower requirements. For example, a 500 horsepower engine with eight injectors would typically require 32 lb/hr injectors. However, it is important to allow for variations and ensure there is room for additional fuel flow.
Fuel type is another important factor in fuel injector selection. Different fuels, such as gasoline, ethanol, and race gases, have distinct properties that impact injector performance. For instance, E85 fuel, known for its higher octane performance, demands a larger injector due to its higher BSFC (Brake Specific Fuel Consumption) value.
Additionally, the plug type of the fuel injector must be compatible with the engine. Over the years, various plug types have been used, with some common styles dominating the market. The Bosch manufacturing generations, such as EV1 (older models) and EV6 (modern and water-resistant), are widely recognised naming conventions.
It is worth noting that the fuel pump plays a crucial role in injector performance. Even the best injector will underperform if the fuel pump cannot deliver the required volume and pressure of fuel. Therefore, when sizing injectors, selecting a suitable fuel pump, such as the Holley Dominator EFI fuel pump, is essential to ensure optimal performance.
In summary, choosing the right fuel injector size involves considering horsepower goals, fuel type, plug type, and the capacity of the fuel pump to deliver adequate volume and pressure. Online calculators and resources can assist in determining the appropriate injector size for specific engine requirements.
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Frequently asked questions
You need to consider your horsepower goal, the fuel type you want to run (e.g. gasoline, ethanol, race gasses, fuel additives) and the plug type.
You can use the term BSFC (brake specific fuel consumption) to translate the horsepower level of an engine to the fuel injector flow rate. The formula for BSFC is: horsepower x BSFC = amount of fuel consumed per hour.
The maximum injector duty cycle should be around 90% max for safe operation.
This depends on which ECU you are running. Your ECU will either be compatible with high or low impedance. You can use an ohm meter across the injectors' plug terminals to determine the impedance.
Some common plug types include Ev1/Jetronic (found on older models), Ev6/USCAR (more modern and common on new injector models), and Denso/Sumitomo (common on imported vehicles).
