6 Important Steps To Buy Upgraded Fuel Injectors In 2023

Purchasing upgraded fuel injectors can be an amazing if not necessary mod for your project car. However, doing so can be often confusing and frustrating especially if you end up buying the wrong ones.

In this article we cover 6 important but simple step you need to look into to make sure you get the best upgraded fuel injectors for your car.

upgraded fuel injectors

Checklist index:

  • 1. Impedance
  • 2. Flow Rating
  • 3. Connector Style
  • 4. Port Size
  • 5. Height
  • 6. Alternative Fuel

checklist to purchase the right upgraded fuel injectors

Purchasing upgraded fuel injectors can be totally worth it and it is far less difficult than it seems. 

There are many points to consider, which makes it appear difficult.  However, all of those points are simple to answer, and some of them, as we will see later, can even be calculated using online tools.

As long as you cover all of the points on the list below, you will be well on your way to producing more power with your new upgraded fuel injectors.

1. upgraded fuel injectors Impedance 

Simply put, impedance is how much current your injectors require to function. 

Your injectors are basically solenoids and the courant necessary to activate them is categorized as either high or low impedance.

Low impedance

Low-impedance fuel injectors are commonly used for high-performance applications where fuel demand is high. The biggest advantage of this type of upgraded injector is its ability to open and close much faster.

This type of upgraded fuel injector usually requires about 6-12 amps to initially open but can be reduced to approximately 1-3 amps to stay open afterward.

This lower coil resistance in a low impedance injector allows the internal spring pressure that holds the pintle closed to be increased so the injector can be shut off more quickly.

This makes for much easier tuning of the injector, particularly if it’s a large, high-flow injector.

The type of electric circuit used for low impedance application is commonly referred to as a “peak and hold” circuit. This system is more complex and requires a resistor pack to protect your ECU from high current spikes.

High impedance

High-impedance fuel injectors are the most common OEM type of injectors. Their popularity amongst manufacturers comes from the simplicity of the system and the low manufacturing cost.

This type of fuel injector only requires a single constant amperage level (approximately 11-12 amps) to open and stay open.  Therefore, there is no need for any resistors.

These types of fuel injectors, on the other hand, tend to reach higher temperatures due to their higher amperage demand. They may also be more difficult to tune due to their slower opening and closing times.


Your impedance style (Low or High) is determined by your ECU. 

It is very important to not mix components from high and low impedance to avoid problems or damages. 

Quick tip: You can determine the courant necessary for your injectors by measuring the resistance in ohms across the terminals found on your fuel injector. (1)

2. Flow rating

Fuel Injectors are sized by their flow rate. 

Flow rate is a measurement of how much fuel can be delivered over time. 

It is listed in pounds per hour (lbs./hr.) or cubic centimeters per minute (cc/min.).

To calculate the required flow rate for your upgraded fuel injector, you can use the following formula:

  • (Horsepower X BSFC) ÷ (number of injectors X injector duty cycle) = Flow rate

The flow rate of an injector kit is something that can also be calculated with online tools.

pressure tuning

Furthermore, fuel pressure has an important effect on the flow rate of your injectors.

When there is more pressure in your system, there is more force pushing the fuel out of your injectors. As a result, as pressure increases, so does the amount of fuel that passes through the open injector, and vice versa.

Ultimately, while acquiring upgraded fuel injectors, it is critical to consider the pressure the injectors are rated at as well as your system pressure. This ensures that you do not purchase injector flow rates that are too small or too big.

You can use the following online calculator or formula to compute the flow rate with a certain fuel pressure.

  • [Advertised Flow Rate] X [The Square Root of (Your Pressure ÷ Rated Pressure)]

Quick tip: If no upgraded fuel injector kit fits your needed fuel rate criteria, you can fine-tune the rate of an injector with pressure changes.  

Getting the appropriate amount of fuel flow may be as simple as adjusting the pressure regulator.

Note: It should be noted that adjusting the fuel system pressure is only intended to make minor changes to the injector flow rate. If you need to make major adjustments, larger injectors are probably required.

What is bSFC

BSFC stands for Brake Specific Fuel Consumption and it changes with engine load and rpm.

It tells you how much fuel your engine will use per hour for each horsepower it makes.

Your BSFC can only be determined on a dyno with the following formula:

  • BSFC = lbs. of fuel used per hour ÷ horsepower

However, when doing approximate calculations, the following table from Summit Racing can give you a good number reference.

Naturally Aspirated Engines (N/A)0.45-0.50.63-0.700.9-1.0
Forced Induction Engines0.6-0.650.84-0.911.2-1.3
Nitrous Oxide Engines (NOS)0.6-0.750.84-1.051.2-1.5

What is Duty Cycle 

The duty cycle refers to the amount of time your upgraded fuel injector is activated vs the amount of time it isn’t This is expressed as a percentage, therefore 50% duty cycle means that the injector is held open and closed for the same amount of time.

A suitable injector should have a duty cycle of 80%-85%. Anything larger than that may result in fuel delivery problems.

Static (wide open, or 100% duty cycle) refers to an injector that is always active. In a functioning motor, injectors should not become static. If an injector is always open, it can no longer control fuel delivery.

This could indicate that the injector is too small for the engine’s requirements.

3. Connector style

The connector style refers to the size and pattern of the electric connector on your upgraded fuel injectors.

For obvious reasons, it is important you buy performance fuel injectors with a matching connector style to your current stock or upgraded fuel injector wiring. 

4. upgraded fuel injectors Port Size

The port insert size of your upgraded fuel injectors should be big enough to create a leakproof seal against your stock or upgraded fuel rail and your injection port.

Yet, you don’t want it too tight to not cause damage to your o ring seal when installing it.

5. upgraded fuel injectors Height

It is important to have upgraded fuel injectors with the proper height for fitting.

The standard injector height is: 34mm, 48mm, 60mm.

Many adapters exist to adjust the height of injectors however buying the proper height the first time can avoid headaches.

6. Alternative fuel

If you’re familiar with alternative fuels, you’re probably aware that, while E85 offers several advantages in terms of higher octane number performance, it also need a significantly larger injector due to the fuel’s about 30% higher BSFC number.

This is because burning a pound of pure ethanol produces only around 70% of the heat produced by burning a pound of gasoline.

This implies that ethanol requires around 30% more fuel to generate the same amount of heat, which directly translates to cylinder pressure and horsepower.

As a result, automatically sizing an injector for use with E85 will necessitate an injector that is at least 30% larger.

When calculating injector size for a naturally aspirated engine on E85, we must take the 0.70 BSFC number from the BSFC chart above.

upgraded fuel injector recomendations

If you are thinking about buying aftermarket fuel injectors for your car whether it is for performance goals or simply replacing old ones we recommend checking out our latest article.

4 best aftermarket fuel injectors for your car (brand reviews)

In this article, we go over 4 different brands of aftermarket fuel injectors to help you narrow down the right one for you and your car.

Brand list:

  • Bosch
  • Fuel Injector Clinic
  • Holley
  • Delphi


In conclusion, because of the numerous things to consider, purchasing the proper improved fuel injectors may appear difficult at first. However, by addressing the key points discussed, the process becomes much simpler.

First and foremost, understanding the injector impedance is critical. Low-impedance injectors are appropriate for high-performance applications because they open and close rapidly, whereas high-impedance injectors are more common and cost-effective but have slower response times. Matching the impedance to your ECU is essential to avoid compatibility issues.

Furthermore, the flow rating of the injectors must be determined, which can be done using online tools or calculations based on horsepower, BSFC, number of injectors, and injector duty cycle. Adjusting the fuel system pressure can also fine-tune the injector flow rate.

Other considerations for optimal installation and compatibility include connector style, port size, and height.

By following these guidelines and choosing the proper updated fuel injectors, you can accurately improve your car’s performance while avoiding any potential issues.