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The size of a fuel injector is critical for performance and tuning control. The size of a fuel injector is determined by its flow rate, which is a measure of how much fuel can be delivered over time. This is usually measured in pounds per hour (lbs/hr) or cubic centimetres per minute (cc/min). The right size injector can supply enough fuel under full load conditions at an 80% duty cycle. This allows the injector to close 20% of the time at WOT, preventing it from overheating. While there is no clear difference between 600 and 800 injector fuels, it is important to note that the size of the injector will depend on the engine's specific requirements.
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What You'll Learn
Fuel injector sizing
Fuel injectors come in a variety of sizes, from 105 lbs/hr to 850 lbs/hr. For example, a typical high impedance Holley injector is rated at 42 lbs/hr. The right size injector can supply enough fuel under full load conditions at an 80% duty cycle, which allows the injector to close 20% of the time at WOT, preventing it from overheating.
When choosing the right fuel injector size, it is important to consider the specific application and engine setup. Bigger fuel injectors do not always equate to more power, and using larger injectors without the necessary modifications can lead to engine damage. Excess fuel can flood the engine, causing it to run too rich and potentially damaging spark plugs and the engine itself.
To accommodate larger fuel injectors, modifications such as increasing airflow (through turbochargers or superchargers), installing a bigger throttle body or exhaust, and remapping the computer may be necessary. It is also crucial to consider whether the engine is turbocharged or supercharged and the type of fuel being used, such as E85 or standard pump petrol.
Additionally, the fuel injector control system plays a significant role in injector sizing. For instance, the FT600, FT550, FT550LITE, and FT450 engine management systems from FuelTech can handle a wide range of injector sizes, even the massive 850 lbs/hr injectors found in super-high horsepower applications.
In summary, selecting the appropriate fuel injector size is crucial for optimal engine performance and tuning control. It requires careful consideration of various factors, including the desired horsepower, engine modifications, and fuel type. Consulting with a reputable car tuner and utilising tools such as the FuelTech Fuel Injector Calculator can aid in determining the right injector size for a specific application.
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Fuel injector types
Fuel injectors are sized by their flow rate, which is a measurement of how much fuel can be delivered over time. The flow rate is listed in pounds per hour (lbs/hr) or cubic centimeters per minute (cc/min). The right size injector can supply enough fuel under full-load conditions at an 80% duty cycle, allowing the injector to close 20% of the time at WOT and preventing it from overheating.
There are several types of fuel injectors, and they can be broadly categorized into four main types:
Single-Point Fuel Injection
This is the oldest and simplest form of the fuel injection system. It replaces the carburettor with one or two fuel-injector nozzles in the throttle body, which is the throat of the engine's air intake manifold. This is also called throttle body injection (TBI). While it is not as precise as other systems, it meters fuel with better control than a carburettor and is less expensive and easier to service.
Multi-Point Fuel Injection (MPFI)
This system devotes a separate injector nozzle to each cylinder, right outside its intake port, so it is also called port injection. Every injector sprays fuel at the same time, and each cylinder gets a more precise volume of fuel, with less possibility of fuel condensation outside the intake manifold.
Sequential Fuel Injection
Also called sequential port fuel injection (SPFI) or timed injection, this is a type of multiport injection. While basic MPFI employs multiple injectors, they all spray their fuel at the same time or in groups. Sequential fuel injection triggers each injector nozzle independently, spraying fuel immediately before or as their intake valve opens.
Direct Fuel Injection
This system injects fuel directly into the combustion chambers, past the valves. It is more common in diesel engines but is also used in petrol engines, where it is known as GDI (gasoline direct injection). All the fuel is directly injected into the cylinder, producing maximum fuel economy.
Other types of injectors include high and low impedance injectors. Low impedance injectors require a peak-and-hold injector driver, which allows for a higher opening current and a lower current after the injector is open.
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Fuel injector flow rate
Fuel injectors are sized by their flow rate, which is a measurement of how much fuel can be delivered over time. The flow rate is listed in pounds per hour (lbs/hr) or cubic centimeters per minute (cc/min).
The right size injector can supply enough fuel under full-load conditions at an 80% duty cycle. This allows the injector to close 20% of the time at WOT, preventing it from overheating. An injector of this size can also provide an accurate amount of fuel at low rpm.
To calculate the required flow rate, use the following formula: (Horsepower X BSFC) ÷ (number of injectors X injector duty cycle). For example, a naturally aspirated 300 hp engine (BSFC 0.5), with 8 injectors will need a flow rate of 23.4 lbs/hr. of fuel per injector at an 80% (or 0.8) duty cycle.
It's important to note that the flow rate of a fuel injector can be influenced by the fuel pressure. Increasing the fuel pressure will also increase the amount of fuel that flows through the injector. However, simply doubling the fuel pressure will not double the flow rate; it will only produce 1.4 times as much fuel. Therefore, correct injector sizing is critical, and it is not advisable to raise the differential pressure to achieve the desired flow rate.
FuelTech offers a Fuel Injector Calculator to assist users in selecting the proper fuel injector size. This calculator takes into account the number of fuel injectors, estimated horsepower, and the type of induction. It is important to select the correct fuel injector size to ensure optimal performance and tuning control.
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Fuel injector pressure
Fuel injectors are sized by their flow rate, which is a measure of how much fuel can be delivered over time. This flow rate is calculated by the quantity of fuel flowing to the injector (volume), the force behind the volume of fuel flowing to the injector (pressure), and the injector duty cycle or on-time command from the PCM (pulse width). The flow rate is measured in pounds per hour (lbs/hr) or cubic centimeters per minute (cc/min).
The pressure inside the rail, known as rail pressure, is the pressure inside the fuel rail that delivers fuel from the pump to the injectors. Rail pressure is increased by the pump pressurizing the fuel. The pressure sensor in the rail measures the pressure and sends a signal back to the engine control unit (ECU), which indicates the current pressure in the rail. The ECU then uses a control algorithm to integrate the measurements and actuators to achieve the desired fuel rail pressure.
Effective pressure, or differential pressure, is the actual applied pressure for the injector. It is the pressure differential across the injector. Effective pressure is what the injector flow rate is based on. When an engine is idling, there is a vacuum in the intake manifold, which pulls fuel out of the injectors and increases the effective pressure. When a supercharged or turbocharged vehicle is in boost, the pressure inside the manifold pushes fuel back into the injector, resisting the flow and decreasing the effective fuel pressure.
The proper fuel injector size is critical for performance and tuning control. Fuel injector sizing depends on the specific application, such as the number of fuel injectors, estimated horsepower, and the type of induction. To ensure the correct fuel injector size, it is important to consider the flow rate and pressure requirements of the specific engine.
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Fuel injector control
Fuel injectors are sized by their flow rate, which indicates the amount of fuel delivered over time. This flow rate is measured in pounds per hour (lbs./hr.) or cubic centimeters per minute (cc/min.). Proper sizing ensures the injector can supply sufficient fuel under full load while preventing overheating. The formula for calculating the required flow rate is: (Horsepower X BSFC) ÷ (number of injectors X injector duty cycle). For instance, a 300 hp engine with 8 injectors would need 23.4 lbs./hr. of fuel per injector at an 80% duty cycle.
FuelTech's Fuel Injector Calculator aids in selecting the appropriate fuel injector size for naturally aspirated and turbo engines using gasoline, alcohol, or ethanol. It considers factors such as the number of fuel injectors, estimated horsepower, and induction type. The FT600, FT550, FT550LITE, and FT450 engine management systems from FuelTech can handle a wide range of injector sizes, even accommodating the large 850 lb/hr injectors found in high-horsepower applications.
Additionally, fuel injectors can be categorized into high and low impedance types. High impedance injectors, commonly used in street applications, have a resistance value of around 12 ohms and draw a continuous current of about 1 amp. Low impedance injectors, on the other hand, require a peak-and-hold injector driver, which facilitates a higher opening current and a lower maintenance current. These injectors are often found in aftermarket ECUs and excel in high-fuel-pressure environments.
It is crucial to choose the right fuel injectors for your engine. Selecting overly large injectors can lead to engine flooding and damage, as the excess fuel causes the engine to run too rich. Conversely, smaller injectors may not deliver enough fuel, resulting in sluggish performance or piston damage. Therefore, understanding factors like horsepower, turbocharging, and fuel type is essential for making an informed decision about fuel injector size.
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