Mercedes Mullins
Choosing the right fuel injector is critical for engine performance. Fuel injectors are rated to deliver a specific amount of fuel at a rated pressure, and the size of the injector is determined by the horsepower goal, fuel type, and plug type. The industry standard for fuel injector flow rate is 43 psi/3 bar, and injector flow is typically conveyed in cc's per minute (cc/min) or pounds per hour (lb/hr). For example, a 1000cc injector at 43 psi can deliver 1000 cc of fuel per minute or 96 lb of fuel per hour. As a general rule of thumb, you need 1 cc/min flow for each horsepower, and for ethanol-based fuels, you need to add 30% as they require more fuel to produce the same power.
| Characteristics | Values |
|---|---|
| Fuel Injector Sizing | Critical for performance and tuning control |
| Fuel Injector Flow Rate | Conveyed in cc's per minute (cc/min) or pounds per hour (lb/hr) |
| Fuel Injector Calculation | 1 cc/min flow for each horsepower |
| Fuel Injector Sizing Example | 1000 crank horsepower on 93 octane gasoline, using a fuel pressure of 43 psi requires a 1000cc injector |
| Fuel Injector Body Style | 34mm, 48mm, or 60mm |
| Fuel Injector Plug Type | USCAR (ev6), Jetronic (ev1), Denso (Sumitomo) Multec (Mini-Delphi) |
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What You'll Learn
Fuel injector flow rate
When discussing fuel injectors, the term "a thousand cc injector" refers to a flow rate of 1000cc/min, which is equivalent to 96lb/hr. This illustrates the significant difference between the two measurement units. It is also important to note that the flow rate of an injector can be influenced by the fuel pressure. As fuel pressure increases, the amount of fuel flowing through the injector also tends to increase.
Determining the correct fuel injector flow rate is essential for optimal vehicle performance and tuning control. A general rule of thumb for gasoline engines is to have 1cc/min flow for each horsepower. For example, to achieve 1000 crank horsepower on 93 octane gasoline with a fuel pressure of 43 psi, a 1000cc injector is required. This rule can also be applied to ethanol-based fuels like E85, but it is important to remember that ethanol requires 30% more fuel to generate the same amount of power.
To simplify the process of selecting the appropriate fuel injector, companies like FuelTech offer online calculators. These calculators allow users to input parameters such as the number of fuel injectors, estimated horsepower, and fuel type to receive recommendations for the proper fuel injector sizing. Additionally, these calculators can work backward, determining the maximum horsepower rating of fuel injectors based on their sizing and other factors.
It is worth noting that the flow rate of a fuel injector can be influenced by various factors, including the pressure at which it is tested. Therefore, it is recommended to use a flow rate calculator to adjust the flow rate to the desired pressure. By entering the known flow rate and the desired pressure, users can calculate the expected flow rate at the new pressure.
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Fuel type
The fuel type is a key consideration when choosing a fuel injector. The type of fuel you want to run, such as gasoline, ethanol, race gases, and fuel additives, will impact the size and flow rate of the injector you need.
For example, if you are aiming for 1000 crank horsepower on 93 octane gasoline with a fuel pressure of 43 psi, you will require a 1000cc injector. This same rule of thumb can be applied to ethanol-based fuels, but it is important to remember to add 30% as ethanol requires a greater volume of fuel to generate the same power.
Another example is the general rule of thumb for gasoline: "one CC per hp". This rule can also be applied to ethanol, but with a 30% reduction: "one CC per hp and drop 30% for ethanol".
The type of fuel injection system also needs to be considered when choosing a fuel injector. The main types of fuel injection systems are single-point, multi-point, sequential, and direct injection. Single-point injection is the simplest and oldest type, where one or two fuel injector nozzles are placed in the throttle body. This type of system is less precise and may cause a rough ride at high RPMs due to a lack of fuel supply. Multi-point fuel injection (also known as port injection) provides a separate injector nozzle for each cylinder, ensuring that the fuel is drawn completely into the cylinder. Sequential injection is the most common and effective system, where each nozzle is coordinated with its cylinder phase, spraying fuel only when the intake valve opens. Direct injection is the most precise method, injecting fuel directly into the combustion chamber, and is more common in diesel engines but is also used in some gasoline engines.
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Fuel injector sizing
The industry standard for fuel injector flow rate is 43 psi/3 bar, and the flow is typically conveyed in cc's per minute (cc/min) or pounds per hour (lb/hr). For example, a 1000cc injector at 43 psi can deliver 1000 cc of fuel per minute or 96 lb of fuel per hour. A simple rule of thumb for sizing a gasoline injector is to have 1 cc/min flow for each horsepower. This rule can also be applied to ethanol-based fuels, but with a 30% increase in fuel volume to account for the lower energy density of ethanol.
Modern fuel injectors come in various external dimensions or "body styles", with the most common sizes being 34mm, 48mm, and 60mm. The Bosch ev14 compact, a popular choice for motorsport injectors, falls into the 34mm category. The 48mm size is often referred to as the ev14 medium or mid-length and is commonly found in GM race-based vehicles like the LS2.
To aid in the selection process, companies like FuelTech offer fuel injector calculators. These calculators allow users to input parameters such as the number of fuel injectors, estimated horsepower, and type of induction to receive recommendations for fuel injector sizing. Additionally, these calculators can determine the maximum horsepower rating of fuel injectors by working backward from the sizing and other given parameters.
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Fuel injector body style
Fuel injectors are a critical component of an engine's performance and tuning control. The injector is located in the combustion chamber, inlet manifold, or throttle body, and its function is to spray fuel into the air inside the cylinder or combustion chamber.
The "body style" of a fuel injector refers to its external dimensions. While there is no industry standard for injector sizing, modern fuel injectors typically fall into one of three sizes: 34mm, 48mm, or 60mm. The Bosch ev14 compact is a well-known motorsport injector with a 34mm body style. The 48mm size is also known as the ev14 medium or mid-length and is commonly found in the GM race-based LS2 engine. The largest of the three common sizes, 60mm, is less prevalent.
It is important to select the right fuel injector size for your engine, as undersized injectors can compromise performance, while bigger ones may not necessarily improve it. The fuel injector flow rate is a crucial factor to consider when choosing an injector. The industry standard flow rate is 43 psi/3 bar, and it is typically conveyed in cc's per minute (cc/min) or pounds per hour (lb/hr). For gasoline engines, a simple rule of thumb is to have 1 cc/min flow for each horsepower. For example, to achieve 1000 crank horsepower on 93 octane gasoline with a fuel pressure of 43 psi, you would need a 1000cc injector.
Various companies like FuelTech and Holley offer fuel injector calculators to help determine the appropriate injector sizing based on factors such as horsepower, fuel type, and induction type. Additionally, injector harness plug styles vary, with options like USCAR (ev6), Jetronic (ev1), and Denso (Sumitomo) Multec (Mini-Delphi). Bosch, Delphi, Denso, and other manufacturers supply injectors to specific brands, and the body style often indicates the type of connector used.
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Fuel injector control
To simplify the selection process, companies like FuelTech offer a Fuel Injector Calculator. This tool assists users in choosing the appropriate fuel injector size by allowing them to input parameters such as the number of fuel injectors, estimated horsepower, and the type of induction. The FuelTech calculator is versatile, accommodating both naturally aspirated and turbo combinations that run on gasoline, alcohol, or ethanol.
The FuelTech engine management systems are designed to handle a wide range of fuel injector sizes, even the massive 850 lb/hr injectors found in super-high horsepower applications. These systems provide advanced features such as sequential injection, ignition, O2 closed loop, Data Logger, Boost Controller, and Nitrous Controller. Additionally, certain models, such as the FT600, FT550, and FT450, offer touchscreen displays for convenient tuning adjustments without requiring a PC connection.
It is important to note that fuel injector selection goes beyond just the size and flow rate. Other factors, such as horsepower goals, fuel type (gasoline, ethanol, race gases, or fuel additives), and plug type, also come into play. Modern fuel injector manufacturers have made significant strides in adapting their products to a wide range of vehicles, and fuel injector specialists can provide guidance in making the right choice for specific engine requirements.
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Frequently asked questions
For a 900 horsepower engine with a supercharger, a 95 to 100 lb/hr injector is a good starting point. This can be calculated by multiplying the horsepower by the BSFC number, and then multiplying that number by the engine duty cycle safety margin.
For a standard Chevy truck engine from the "LS" family, a 2100cc/min injector would be required if using a fuel pressure of 43psi.
There are many factors to consider when determining the right fuel injector size for your engine. These include the horsepower goal, the type of fuel, and the plug type. It is critical to select the proper size for optimal performance and tuning control.
