How to choose the right injectors for your engine

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How to choose the right injectors for your engine

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

4 Cylinders 6 Cylinders 8 Cylinders
HP cc/min cc/min cc/min
200
328
219
164
300
492
328
246
400
657
438
328
500
820
547
410
600
984
657
492
700
1149
766
574
800
1312
864
657
900
1477
984
738
1000
1641
1093
820
1100
1804
1203
902
1200
1969
1312
984


Petrol, NA

4 Cylinders 6 Cylinders 8 Cylinders
HP cc/min cc/min cc/min
200
295
197
148
300
443
295
221
400
591
394
295
500
738
492
369
600
886
591
443
700
1034
689
517
800
1181
778
591
900
1329
886
664
1000
1477
984
738
1100
1624
1083
812
1200
1772
1181
886


E85 Turbocharged or Supercharged

4 Cylinders 6 Cylinders 8 Cylinders
HP cc/min cc/min cc/min
200
426
285
214
300
640
426
319
400
854
569
426
500
1066
711
533
600
1280
854
640
700
1493
995
747
800
1706
1124
854
900
1920
1280
959
1000
2133
1421
1066
1100
2346
1564
1173
1200
2559
1706
1280


E85 NA

4 Cylinders 6 Cylinders 8 Cylinders
HP cc/min cc/min cc/min
200
384
256
192
300
576
384
287
400
768
512
384
500
959
640
480
600
1152
768
576
700
1344
896
672
800
1535
1011
768
900
1728
1152
863
1000
1920
1279
959
1100
2111
1408
1056
1200
2304
1535
1152

 

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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  • Benjamin Attard