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There is a lot of misinformation surrounding fuel injector upgrades. Changing fuel injectors is not a “plug-and-play” performance upgrade, such as installing a low restriction air filter. It’s something that requires knowledge about how the fuel delivery system works.

In fact, upgrading fuel injectors may actually decrease the engine power if done incorrectly.

The objective of this article is to shed light on this important topic by explaining under what circumstances it is necessary to upgrade the injectors and how to do it properly.

What is the air-fuel ratio?

At its core, the efficiency of internal combustion engines is determined by the air-fuel ratio (AFR). As its names imply, the air-fuel ratio is the relation between the mass of air entering the engine to the mass of fuel used during combustion. For example, an AFR of 5:1 means 5 parts of air per each part of fuel.

There are a few known air-fuel ratio inflection points that engineers have already established under laboratory conditions:

  • Maximum engine power: is achieved when the AFR is 12.6:1
  • Perfect combustion (no pollution): is achieved when the AFR is 14.7:1 
  • Best fuel economy: is achieved when the AFR is 15.4:1 

You may be wondering, what air-fuel ratio has to do with fuel injector upgrades? The answer is simple. When you install certain engine upgrades such as a turbocharger you are automatically increasing the amount of air entering the engine and thus, you should compensate it increment fuel delivery to maintain the optimal AFR. 

Toyota New Fuel Injector
Toyota Fuel Injector

What is a fuel injector upgrade?

A fuel injector upgrade consists of replacing the stock injectors with a new set capable of delivering a higher flow rate. For example, think of a Ford Mustang with a 4.6-liter engine. The stock fuel injectors are good enough to deliver an adequate amount of fuel to the stock engine under any driving condition. Now visualize the same engine with a supercharger fitted to it. Stock fuel injectors won’t be able to supply enough fuel anymore meaning that the optimal air-fuel ratio of 12.6:1 required to obtain maximum power will be out of reach. Any modification resulting in an increased amount of air entering the combustion chamber will necessarily need compensation on the fuel delivery side. 

In other words, you’ll need to match your fuel injector set according to the airflow entering the engine. That way you can ensure an adequate amount of fuel to make the engine perform as intended. 

It’s at this point that many enthusiasts get confused. The objective is not to alter the air-fuel ratio, on the contrary, it’s to ensure it can be maintained. Maximum engine power will always be achieved with an AFR of 12.6: 1. If you install injectors with an improper flow rate (too high or too low) you may end up hindering performance.

Who needs fuel injector upgrades?

By now you may have a hint of the kind of modifications requiring a fuel injector upgrade. However, sometimes could be harder to know if an injector upgrade would be necessary since each engine/injector design is different. For your convenience, we grouped the possible scenarios into three categories.

You will definitely need a fuel injector upgrade after installing a:

  • Turbocharger
  • Supercharger
  • Nitrous oxide injection system (NOS)

You will probably need a fuel injector upgrade after installing:

  • Performance exhaust headers
  • Hi-performance cam upgrade
  • Modified/Reprogrammed Electronic Control Module (ECM)
  • Modified and/or larger diameter Mass Air Flow sensor (MAF)

You may benefit from a fuel injector upgrade, but not necessarily need it, after installing:

  • Enhanced intake manifold
  • A low-restriction air intake system
  • Performance cylinder heads

The above should only be used as a guideline. Depending on your vehicle the stock fuel injectors may be all you need. Always consult an expert technician when in doubt.

Are high-performance injectors enough?

You have to keep in mind that performance-wise your goal is achieving the magic “12.6:1” air-fuel ratio. Undoubtedly, high-performance injectors help but depending on the level of power you seek they might be not enough. Replacing a set of stock 500cc injectors with high-performance 1000cc injectors does not mean that you automatically doubled the fuel delivery. It’s a bit more complicated than that.

In many cases, high-performance injectors exceed the flow capacity of the vehicle’s stock fuel pump. To ensure your engine can handle the extra power you may need to upgrade/install other components such as:

  • High flow electric fuel pump
  • Adjustable fuel pressure regulator
  • Reprogrammed ECU / Hi-performance MAF sensor

High-performance injectors maintenance

NOTE: Using fuel injectors with the wrong capacity can be detrimental to your engine.

If you are investing in high-performance injectors and other related engine upgrades, then you should be willing to maintain them properly. It’s suggested to perform professional fuel injection system maintenance every 20,000 miles as a minimum. Due to the nature of high-performance fuel injectors, ultrasonic cleaning is highly advised as well as a test to ensure they are delivering the intended flow rate.

Updated on 04/13/2022

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