Sylvie Willis
Choosing the right size of fuel injector is critical for performance and tuning control. It can be challenging to determine the size and flow rate of a fuel injector as there are many factors to consider. These include the horsepower goal, fuel type, injector harness plug style, and injector body style. To simplify the selection process, FuelTech and Snake Eater Performance offer online calculators that can recommend the appropriate fuel injector sizing based on user inputs such as horsepower, fuel type, and induction type.
Fuel Injector Sizing
| Characteristics | Values |
|---|---|
| Fuel Type | Gasoline, Ethanol, Race Gasses, Methanol, etc. |
| Horsepower | 500 hp, 900 hp, 1000 hp, etc. |
| Fuel Pressure | 43 psi, 60 psi, etc. |
| Injector Size | 34mm, 48mm, 60mm |
| Injector Flow Rate | 31.25 lb/hr, 32 lb/hr, 73 lb/hr, 95 lb/hr, 100 lb/hr, etc. |
| Fuel Injector Calculator | FuelTech, Holley, Fuel Injector Clinic |
| Injector Harness Plug Style | USCAR (ev6), Jetronic (ev1), Denso (Sumitomo), Multec (Mini-Delphi) |
| Fuel Pump | Holley Dominator EFI Fuel Pumps |
| Fuel Injector Control | FuelTech FT600, FT550, FT550LITE, FT450 |
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What You'll Learn
Fuel injector sizing calculators
To calculate the necessary fuel injector size, different calculators use different parameters. The Fuel Injector Size Calculator by POWERNATION uses a formula that factors in the estimated maximum horsepower, brake-specific fuel consumption (BSFC), and the number of cylinders. The formula involves multiplying the estimated maximum horsepower by the BSFC and then dividing that product by the result of multiplying the number of cylinders by 0.8. The 0.8 factor represents an 80% duty cycle, a common safety margin that prevents the injectors from constantly operating at full capacity.
The MAPerformance Fuel Injector Calculator requires you to input your goal crank horsepower, the number of injectors (cylinders) in your engine, the correct number based on the aspiration of your engine, and the goal PSI at the rail. It also assumes a 1:1 rising rate fuel pressure regulator for turbo applications.
Another calculator, the Injector Dynamics Fuel Flow Calculator, takes a different approach by estimating airflow based on known parameters and then directly calculating fuel flow from the exhaust lambda. This method does not rely on Brake Specific Fuel Consumption (BSFC), which is rarely measured and can be affected by various factors that impact engine efficiency.
It is important to ensure accuracy when using fuel injector sizing calculators, as the correct fuel injector size is critical for optimal engine performance and preventing fuel-related issues.
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Injector fit
Fuel Injector Sizing
Determining the correct size of fuel injectors depends on several factors, including the horsepower goal, fuel type, and plug type. It is recommended to use a fuel injector sizing calculator or follow specific guidelines for different fuels. For example, when sizing injectors for gasoline, a simple rule of thumb is to allow for 1cc/min flow for each horsepower. So, if you aim for 1000 crank horsepower on 93 octane gasoline with a fuel pressure of 43 psi, you would require a 1000cc injector. For ethanol-based fuels like E85, it is important to add 30% to the calculation since ethanol demands a higher volume of fuel to generate the same power.
Fuel Injector Flow Rate
The flow rate of fuel injectors is another crucial factor. While there is no universal industry standard, the commonly accepted flow rate is 43 psi/3 bar. It is worth noting that fuel injector flow rate sizing is typically the first consideration when determining the appropriate injector for a specific application.
Fuel Injector Body Style and Size
Fuel injectors come in various body styles and sizes. Modern injectors typically fall into three main sizes: 34mm, 48mm, and 60mm. The size of the injector will impact the ease of installation and the available mounting options. For example, the 60mm size is popular because it allows for easier adjustment of the fuel rail compared to shorter injectors, which may require custom mounts.
Fuel Pump Capacity
When sizing fuel injectors, it is crucial to consider the capacity of the fuel pump to ensure it can deliver the required volume and pressure of fuel to the injectors. Even the most efficient injector will not function optimally if the fuel pump cannot meet its demands.
Fuel Injector Specialist
If you encounter challenges in making the injectors fit, it is advisable to consult a fuel injector specialist. They can provide expert guidance and offer adaptation solutions to ensure the injectors are properly fitted and functioning as intended.
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Fuel type
Fuel injectors are available for a variety of fuel types, including gasoline, ethanol, methanol, race gasses, and fuel additives such as MTBE or Oxygenators. The type of fuel you want to run will impact the size and flow rate of the injector you need.
For example, if you are using gasoline, the standard fuel injector flow rate is 43 psi/3 bar. However, if you are using a fuel with a higher octane number, such as E85, you will need a larger injector because it demands a roughly 30% higher BSFC (Brake-Specific Fuel Consumption) number.
Additionally, the horsepower of your engine will also impact the size of the injector you need. For instance, a 500 horsepower engine would theoretically require a 32 lb/hr injector, while a 900 horsepower engine would need a 95-100 lb/hr injector.
It's important to note that bigger injectors do not always equal more power. If your engine is not set up to handle the extra fuel, it can lead to flooding, fouled spark plugs, and engine damage. Therefore, it's crucial to consider the fuel type, horsepower, and other factors when determining the appropriate size and flow rate of a fuel injector.
To make the selection process easier, there are fuel injector calculators available online, such as the one offered by FuelTech, which can help you determine the proper fuel injector size for your specific application.
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Injector flow rate
To calculate the required flow rate, one must consider the engine's horsepower and the number of injectors. For example, to achieve 500 hp with eight injectors, each injector would need to deliver 31.25 lb/hr. However, this simplified calculation doesn't account for variations in engine performance and additional fuel flow requirements. Therefore, it is recommended to use a duty cycle safety margin, typically around 70%, which allows for potential errors and ensures optimal injector performance.
For boosted engines with injectors located in the intake manifold, it is beneficial to size the injectors larger than the calculated value. This is because the injectors have to work against higher pressures, which can reduce fuel pressure in the fuel rail. For instance, a 900 horsepower engine with a supercharger making 15 psi of boost would require a 95-100 lb/hr injector as a starting point.
Additionally, the type of fuel used can impact the required injector size. Alternative fuels, such as E85, may demand a larger injector due to higher BSFC (Brake-Specific Fuel Consumption) numbers. It is also crucial to consider the fuel pump's capacity to deliver fuel at the required volume and pressure to ensure the injectors can perform effectively.
Several online tools, such as the FuelTech Fuel Injector Calculator, can assist in determining the appropriate injector sizing for various engine configurations and fuel types. These tools take into account factors such as horsepower, the number of injectors, and the type of induction to recommend the suitable injector size.
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Horsepower goals
When determining the right size of fuel injectors for your horsepower goals, there are several factors to consider. The amount of fuel an engine requires to produce one horsepower in an hour is measured in pounds of fuel per horsepower per hour (lbs/hp/hr), commonly abbreviated to lbs/hr. This is an important metric when selecting fuel injectors.
The conventional BSFC (Brake Specific Fuel Consumption) number for a gasoline engine is 0.50, meaning the engine burns half a pound of gasoline per hour to make one horsepower. However, with advancements in engine combustion efficiency, this number can often be lower, such as 0.45 or less. Using the simple formula of horsepower multiplied by BSFC, we can determine the required fuel flow. For example, 500 horsepower x 0.5 = 250 lbs/hr of fuel.
If you have a specific horsepower goal, such as 500 horsepower, and an 8-cylinder engine, you would divide the required fuel flow by the number of injectors. In this case, 250 lbs/hr divided by 8 injectors gives us approximately 31.25 lbs/hr necessary to feed the engine. Therefore, a 32 lb/hr injector should, in theory, be sufficient for a 500 horsepower engine.
It is important to note that this calculation assumes a 100% duty cycle, which is not realistic. Injector performance is influenced by how well the injector delivers fuel across its entire flow scale. To ensure adequate performance and tuning control, it is recommended to use a 70% duty cycle or even a more conservative 90% duty cycle. This would mean that a larger injector, such as a 42 lb/hr or 43 lb/hr injector, would be more appropriate for the above example.
Additionally, the type of fuel and engine aspiration (naturally aspirated, turbocharged, or supercharged) can impact your injector size calculation. For example, ethanol-based fuels require approximately 30% more fuel to produce the same power as gasoline. Online calculators and injector manufacturers' resources can provide more precise estimates by taking into account these variables and your specific engine configuration.
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Frequently asked questions
The fuel injector size depends on several factors, including the horsepower goal, fuel type, and plug type. It is critical to select the proper fuel injector size for performance and tuning control.
A simple rule of thumb for sizing your injector for gasoline is to use 1cc/min flow for each horsepower. For example, if you want to make 1000 crank horsepower on 93 octane gasoline, using a fuel pressure of 43 psi, you would need a 1000cc injector.
Modern injectors typically come in three sizes: 34mm, 48mm, and 60mm. However, there is no industry standard, and the size can vary depending on the specific application and engine requirements.
When sizing fuel injectors, it is crucial to consider the fuel pump needed to feed the injectors at the appropriate fuel pressure. Even the best injector will not perform properly if the fuel is not delivered in the required volume and pressure.
Yes, there are online calculators available, such as the Fuel Injector Calculator from FuelTech and the Flow Rate Calculator from Fuel Injector Clinic. These tools can assist in determining the proper fuel injector sizing based on various parameters such as horsepower, fuel type, and engine specifications.
