Sylvie Willis
Fuel injectors are rated to deliver a specific amount of fuel at a rated pressure. The size of a fuel injector is critical for performance and tuning control. To determine the size of a fuel injector, one must consider the engine's power and the type of fuel used. Fuel injectors can be categorised into two main types: high and low impedance. High impedance injectors are the most common selection for street applications and have a resistance value of around 12 ohms. Low impedance injectors, on the other hand, require a peak-and-hold injector driver and are typically used in aftermarket ECUs.
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What You'll Learn
Fuel injector calculators can help determine the right size
Fuel injector calculators are a useful tool to help determine the right size of fuel injector for your engine. FuelTech, for example, offers a calculator that assists racers and builders in selecting the correct fuel injector size. This is critical for performance and tuning control.
The FuelTech calculator allows users to select the number of fuel injectors, input estimated horsepower, and choose the type of induction. It can also work backward, determining the maximum horsepower rating of fuel injectors based on their sizing and other parameters. This is a useful feature for those wanting to know how much power they can make with a specific injector.
The calculator is compatible with naturally aspirated and turbocharged engines that run on gasoline, alcohol, or ethanol. It can also handle stock injectors and those with a high lb/hr rating. The addition of a Peak & Hold driver box to the ECU gives users ultimate control of low impedance fuel injectors, and the calculator is proven in NHRA championship and record-holding racecars.
Another option for determining fuel injector size is to use a Minimum Injector Flow Rate calculator. This estimates the engine airflow under specified conditions and then uses that airflow to estimate the minimum injector flow rate required. This method offers a more precise way of determining the correct injector size compared to horsepower estimates.
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The type of fuel used impacts injector size
The type of fuel used is a critical factor in determining the right injector size for optimal performance and tuning control. For instance, a 4-cylinder turbo car that produces 800-900 whp will require a large injector, such as a 1600-2000cc/min injector, to deliver sufficient fuel. On the other hand, the same car with a smaller injector, like a 1000cc/min injector, may struggle with idle quality and drivability.
Additionally, the choice of fuel influences the injector's operation. When selecting a fuel injector for an alcohol-based application (e85), the injector remains open for a longer duration to deliver the required amount of fuel. This extended opening time often results in better performance on e85 compared to 93 octane fuel.
It is also important to note that injector size is influenced by the engine's setup and modifications. Increasing airflow by installing a turbocharger or supercharger, or using a bigger throttle body, can impact the required injector size. Similarly, if you've added a turbo, a higher-flowing fuel pump, or a bigger exhaust, you may need larger injectors to prevent the engine from running too lean and avoid potential damage to the pistons and motor.
To determine the appropriate injector size, it is recommended to use tools such as the FuelTech Fuel Injector Calculator, which takes into account factors like horsepower, the number of fuel injectors, and the type of induction (naturally aspirated or turbocharged).
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The injector's physical dimensions are important
The injectors' physical dimensions are important because they have changed drastically over the years. The Bosch-style multi-point injectors that first appeared in the GM TPI engines around 1985 are physically the largest and tallest of all the GM injectors. However, these injectors are becoming less popular because they don't deliver the high flow rates demanded by today's more powerful engines.
On the other hand, the Gen IV LS3 style injector is the shortest of the factory squirters, but its size should not be confused with a lack of flow potential as these injectors can deliver a high flow rate. The O-ring diameter of the Gen IV LS3 style injector is also larger than that of its predecessor, the Gen III LS3 style injector. This difference in O-ring diameter is important because using an older engine with a newer injector will require changing the O-rings to the smaller version for the injector to fit properly.
The physical dimensions of the injector are also important when considering the electrical connections. There are three popular electrical connectors that are not interchangeable, so it is important to choose an injector with the correct connectors for your engine. The most popular are EV1, EV6 (USCAR), and Multec 2 connectors, but there are also several import styles.
Additionally, the physical dimensions of the injector can impact the flow rate, which is critical for engine performance. A larger injector can offer a benefit if you decide to boost the power because it can provide enough additional fuel flow to offset the power increase. However, it is important to note that every injector has a maximum operating pressure above which it will not open, and this differs across injectors. Therefore, choosing the right injector size based on realistic estimates of power and how the system will be used is crucial.
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The injector's resistance value is a key factor
Fuel injectors are available in a variety of sizes, and selecting the right size is critical for performance and tuning control. Injector size is determined by factors such as power levels, ECUs, and engine type. For example, a supercharged engine will require larger injectors to flow enough fuel to achieve high power outputs.
The injectors' resistance value is a key factor in determining the injector size and type. Injectors come in two main types: low impedance and high impedance. Low impedance injectors have a coil resistance of 2-4 ohms, while high impedance injectors have a resistance of around 12 ohms. Low impedance injectors are typically used in high-performance applications where a large amount of fuel is needed, while high impedance injectors are better suited for more moderate applications with lower fuel requirements. The higher the impedance, the more the material resists the flow of electricity, and the harder it is on the injector drivers.
The resistance value of an injector can be measured using a standard ohm or voltmeter. It is important to note that the resistance of an injector can change during use, and an injector with a borderline resistance value may drop below the minimum acceptable value after a short period of operation. A low resistance can also be caused by the use of commercial injector cleaners, which can wash off the insulation of the windings. Therefore, it is important to regularly check the resistance of fuel injectors to ensure they are within the acceptable range.
By understanding the resistance value and impedance of fuel injectors, one can make an informed decision when selecting the appropriate injector size and type for a specific application, ensuring optimal performance and efficiency.
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The injector's duty cycle impacts its performance
The injector duty cycle is a calculation representing the amount of time a fuel injector is energised or on during an engine cycle. It is the ratio between the pulse width required for proper AFR and the length of time available to inject that amount of fuel. The injector duty cycle is measured as a percentage, with a 50% duty cycle indicating that the injector is held open and closed for an equal amount of time. When the engine needs more fuel, the time that the injector stays on (its duty cycle) increases, allowing more fuel to flow into the engine.
The duty cycle is dictated by the RPM and the Otto cycle. For example, a 20ms pulse width at 3000rpm is a 50% duty cycle because the 'window of opportunity' is 40ms. However, the same 20ms pulse width at 6000rpm is a 100% duty cycle because the 'window of opportunity' is 20ms. It is important to note that the injector duty cycle should not exceed 100% as it is physically impossible for the fuel to get there. If the injector stays on all the time, it is said to be static or wide open.
The impact of the injector duty cycle on performance is significant. If the injector duty cycle exceeds 100%, it can cause issues such as unpredictable fueling, scattered AFR, fluctuating EGTs, and difficulty in tuning. Additionally, it can stress the injectors beyond their operational range, leading to overheating and possible pre-ignition. Therefore, it is crucial to determine the correct injector size and operate within the safe range of the injector duty cycle to ensure optimal performance and avoid any potential issues.
Furthermore, the injector duty cycle is essential when determining the correct injector size, especially for supercharged engines. Operating at the extreme ends of the output cycle can result in non-linear injector performance, impacting the amount of fuel delivered to the engine. This can have catastrophic consequences for engine survival at WOT. Therefore, a conservative duty cycle is recommended to ensure adequate injector sizing and performance.
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Frequently asked questions
The size of the fuel injector you need depends on the horsepower of your engine. You can use a fuel injector calculator to work out the size you need by entering a few simple details.
You will need to know the number of fuel injectors, the estimated horsepower, and the type of induction.
Using a calculator will save you time and ensure you select the right size for your engine. The correct fuel injector size is critical for performance and tuning control.
All injectors have a part number stamped on the side, which you can type into a search box to find the right one for your vehicle. Alternatively, you can search using your engine code or name.
