When do I need to change/upgrade my Injectors?

If you're hunting for injectors and are wondering:

- How do I know when to change injectors?

- What injector size is the best for my build?

- How to I check the duty cycle?

- How do I check if I am running rich or lean?

- Is there a difference between top feed and side feed injector flow?

Then this section is for you!

Getting the right air/fuel mixture in your engine is paramount to making more power and keeping your engine running well. Quite a few modifications will affect the air delivery in the combustion chamber, and thus the Air/Fuel Ratio (AFR). If your engine runs too rich, you will have increased fuel consumption and might have flooding issues, and if it runs too lean, you can burn out the pistons and destroy your engine. As a main rule of thumb, injectors should not be running over 90% of their duty cycle. Above this threshold, it is recommended to get higher flow ones to make sure your engine does not run lean.

This guide will help you identify if you need to change to higher-flow injectors, and what flow-rate you need for your power goals.

What modifications require a change to bigger injectors?

These are some of the main modifications that will require you to check and/or change your injectors:
- Increase engine compression ratio
- Upgrade of camshafts with 1mm lift or more
- Installation of a forced induction system (turbo, supercharger) on a NA engine
- Upgrade of turbocharger or supercharger pulleys.
- Installation of individual throttle bodies
- Port and polish of engine head
- Installation of bigger valves.
- Installation of a higher flow fuel pump

Variable Valve Timing engines usually require more fuel to be injected, so checking the duty cycle after a mod is a wise precaution to be taken.

How to check if i'm running lean?

The easiest and simplest way to know if your engine is running too lean is to have a look at your spark plugs. You can refer to the guide below to know how your engine is doing based on the state of your spark plugs.

How do I check the duty cycle of my injectors?

The duty cycle is not something easy to determine without the help of a tuner, but it is imperative to upgrade them if their duty cycle at Wide Open Throttle (WOT) exceeds 90% capacity.

Should I just get the biggest injectors I can then?

Biggest is not always better when it comes to injectors, and if the ones you choose are too big, you can have issues such as engine flooding, or fouled spark plugs, and damage your engine.

So how do I find the right injector size for my needs?
This depends on 5 factors:
- Horsepower target
- Engine type
- Injector position
- Aspiration (NA / turbo / supercharged)
- Type of fuel
- Please take note that for side-feed injectors, you need to increase the injector capacity by 15% compared to top feed

Injector Selection Tables

With all these factors established, you can now choose the right injectors for your needs, based on the tables below.
Points to note are:
- Horsepower is at the engine (count a drivetrain loss of 30% if you calculate based on wheel horsepower)
- Injector duty cycle is 80%
- Fuel pressure is 3bar (43.5psi)

Petrol, Turbocharged or Supercharged

Petrol, NA

E85 Turbocharged or Supercharged

E85 NA

Find your Injector Kits here!

If you are looking for ECUs to tune your engine, we have also added the full lineup of Link G4 ECUs here!

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