Ameer Randolph
Choosing the right fuel injector size is critical for performance and tuning control. It can be challenging to determine the size and flow rate of your fuel injector, as there are many factors to consider, including horsepower goals, fuel type, injector harness plug style, and engine RPM. Modern injectors typically fall into one of three sizes: 34mm, 48mm, or 60mm. To determine the appropriate size, individuals can use online calculators or perform manual calculations that take into account factors such as brake-specific fuel consumption (BSFC) and duty cycle.
Characteristics and Values Table for Fuel Injectors
| Characteristics | Values |
|---|---|
| Fuel Type | Gasoline, Ethanol, Race Gasses, Fuel Additives |
| Horsepower Goal | 500, 900, 1000, 2400 |
| Injector Size | 34mm, 48mm, 60mm, 88mm |
| Injector Flow Rate | 43 psi/3 bar is the industry standard |
| Fuel Injector Calculator | FuelTech, Fuel Injector Clinic |
| Fuel Pump | Holley Dominator EFI fuel pumps |
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What You'll Learn
Horsepower
Fuel injector sizing is critical for performance and tuning control. The amount of power you desire will directly affect the amount of fuel you will need to achieve your goal. For example, let's consider a 500 horsepower engine. In theory, a 32 lb/hr injector should be able to feed it. However, the internal workings of an engine are more complex than that. This calculation does not account for additional fuel flow or potential errors.
To ensure optimal performance, it is recommended to be generous with your calculations and use a 70% duty cycle. This means that for a 500 horsepower engine, you would need 31.25 lb/hr necessary to feed the engine (500/8 injectors = 31.25). With a 70% duty cycle, this figure becomes 31.25 x 1.30 = 40.6 or 41 lb-hr injector.
For higher horsepower engines, larger injectors are often needed. For example, a 900 horsepower engine with a supercharger would require a 95-100 lb/hr injector as a starting point. It is also important to consider the fuel pump when sizing injectors, as it needs to feed the injectors at the appropriate fuel pressure.
Additionally, the type of engine and fuel can impact the size of the fuel injector. For instance, a Holley 12-800 inline fuel pump is ideal for normally aspirated EFI engines producing up to 800 horsepower at 43 psi. On the other hand, the Holley Dominator 12-1200 is rated to feed a supercharged 1,000-hp engine at 60 psi.
To determine the correct fuel injector size for your desired horsepower, you can use online calculators that take into account factors such as the number of cylinders, fuel pressure, and engine aspiration. These tools can help you make an informed decision and ensure that your engine performs efficiently.
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Fuel type
Fuel injectors come in many types and sizes, and choosing the right one is critical for performance and tuning control. The wrong choice of fuel injector can cause your engine to run rough or even ruin it altogether.
The first step in choosing the right fuel injector is to consider the fuel type you want to run. Common fuel types include gasoline, ethanol, and race gases. The fuel type will determine the injector's flow rate and size. For example, when sizing injectors for gasoline, a simple rule of thumb is to use 1 cc/min flow for each horsepower. So, if you want to make 1000 horsepower on 93-octane gasoline at 43 psi of fuel pressure, you will need a 1000 cc injector. This rule of thumb can also be applied to ethanol-based fuels like E85, but it is important to remember to add 30% since ethanol requires more fuel to produce the same power.
Another factor to consider when choosing a fuel injector is the injector harness plug style. Common plug types include USCAR (EV6), Jetronic (EV1), Denso (Sumitomo), and Multec (Mini-Delphi). The plug type will depend on the vehicle and the age of the injector, as newer models tend to use more modern plug types.
In addition to the fuel type and plug style, it is also important to consider the injector's size and flow rate. While there is no industry standard, modern injectors typically fall into one of three sizes: 34mm, 48mm, or 60mm. The size of the injector will depend on the specific application and the fuel injector body style requirements.
Finally, it is crucial to ensure that the fuel injector is properly sized and rated to deliver the appropriate amount of fuel at the required volume and pressure. A larger injector does not always mean more power, as an injector that is too big can flood the engine with excess fuel, causing it to run too rich or not at all. On the other hand, an injector that is too small will not be able to deliver enough fuel to the engine, causing it to run too lean and potentially damaging the motor.
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Injector harness plug style
When it comes to injector harness plug styles, there are several types of fuel injector connectors and it can be challenging to determine the right one for your needs. Firstly, you will need to visually identify your type of fuel injector connector and compare it to pictures in catalogues to ensure you get the correct one. Many OEM brands of auto, truck, marine, motorcycle, and ATV applications use their own unique injector connector designs. For example, brands such as GM Delphi, Honda, Nippon Denso, Sumitomo, Nissan, and Toyota use their own injector connector designs.
There are also some universal injector connector types, such as Jetronic/Minitimer, and USCAR. Vehicle manufacturers that are not specifically listed as using their own injector connector designs usually use one of these universal types. However, it is important to note that some major parts suppliers have been found to have inaccurate information regarding make, year, and model applications for fuel injector connectors.
There are also different sizes of injector harness plugs. While there is no industry standard, modern injectors typically fall into one of three main sizes: 34mm, 48mm, or 60mm. The 34mm style is the standard for cutting-edge motorsport injectors, while 48mm is also known as ev14 medium or mid-length and is commonly found on the GM race-based LS2. The 60mm size is highly popular due to the ease of raising a fuel rail with a small shim and longer hardware compared to using a shorter injector.
If you are having difficulty making an injector fit, it is recommended to contact a fuel injector specialist as there are many ways to adapt injectors to get them to fit. Fuel injector connector kits are available that provide all the parts needed to replace, rebuild, or repair broken fuel injector connectors using your existing wiring harness. These kits can be assembled to create a factory-like installed plug, assuring proper electrical conductivity of your F.I. circuit. Alternatively, pre-assembled fuel injector connectors with a 6-inch pigtail are also available for a quick and simple installation.
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Fuel pump
The size of a fuel injector is critical for performance and tuning control. While bigger fuel injectors do not always equate to more power, it is true that unless your engine is set up to handle the extra fuel, the excess fuel will flood the engine. This will cause the engine to either not run or run too rich, leading to fouled spark plugs and engine damage.
To avoid this, it is important to select the right fuel pump. The average advertised weight of a gallon of premium fuel is 6.34 lb/gallon. Brake Specific Fuel Consumption (BSFC) is the projected amount of fuel required to produce 1 HP for 1 hour. This means that an engine with a BSFC of .5 will burn 0.5 lbs of fuel to produce 1 HP for one hour.
Determining the exact BSFC for a specific engine is complicated and requires an engine dyno. Pumping losses are the difference in fuel pressure measured at the fuel pump exit and that of the fuel pressure at the exit of the fuel rail. Friction, fuel line inside diameter, and turns or bends in the fuel line can cause a pressure difference of 4-10 PSI.
FuelTech offers a Fuel Injector Calculator to assist in selecting the proper fuel injector size. This calculator allows users to pick the number of fuel injectors, input estimated horsepower, and the type of induction. It is capable of recommending fuel injector sizing for naturally aspirated and turbo combinations that are run on gasoline, alcohol, or ethanol.
Other factors to consider when choosing a fuel injector size include the maximum injector duty cycle (IDC), the number of cylinders, fuel pressure (PSI), and engine aspiration. It is also important to remember that when sizing injectors, the fuel pump needed to feed the injectors at the appropriate fuel pressure must also be considered.
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Engine type
The size of the fuel injector you need depends on several factors, including the engine type, the fuel type, and the desired horsepower.
For a naturally aspirated engine, the Brake Specific Fuel Consumption (BSFC) is a crucial factor in determining the size of the fuel injector. The BSFC represents the amount of fuel an engine requires 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 is 0.50, which means the engine burns half a pound of gasoline per hour to generate one horsepower. With advancements in engine combustion efficiency and reduced friction, this number can often be lower, such as 0.45 or less. Using the BSFC, you can calculate the amount of fuel needed to achieve your desired horsepower. For example, if you want 500 horsepower, the equation would be 500 horsepower x 0.50 = 250 lbs/hr of fuel.
If you have a supercharged or turbocharged engine, determining the injector size becomes more complex. Both the BSFC and duty cycle numbers become crucial to ensure the injectors are appropriately sized. The duty cycle represents the percentage of time the injector is open during the engine cycle, and it is essential to ensure the injectors can deliver enough fuel to meet the power requirements.
Additionally, the type of fuel you plan to use is a significant consideration. For example, ethanol-based fuels like e85 require a 30% increase in fuel injector size compared to gasoline because ethanol requires more fuel to produce the same power.
To simplify the process of selecting the correct fuel injector size, companies like FuelTech and Holley offer online calculators. These calculators consider factors such as the number of fuel injectors, estimated horsepower, fuel type, and induction type to recommend the appropriate injector sizing.
It is important to note that modern fuel injectors come in various sizes, but the most common dimensions are 34mm, 48mm, and 60mm. The height of the injector and its electrical connector are also factors to consider when making your selection.
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Frequently asked questions
FuelTech offers a Fuel Injector Calculator to help determine the right fuel injector size for your engine. This is critical for performance and tuning control.
A 32 lb/hr injector should feed a 500 horsepower engine. If you want to be more precise, you can use the formula horsepower x BSFC (500 x 0.5 = 250 lbs/hr of fuel) and then divide that by the number of injectors.
This depends on the model and engine size. For example, a 1991 Chevy Silverado 5.7-liter engine has a 350 injector on the left side of the throttle body.
The stock LS1 fuel injectors are 28.6 lb/hr.
