A fuel injector has one of the most important jobs on any electronically fuel injected engine. They are responsible for supplying the fuel to the engine, but more importantly they must be able to inject the fuel in a finely atomised mist, and accurately deliver the right amount of fuel based on the engine’s requirements.

Frequently Asked External Injector Questions

  • Why do you need larger injectors?
  • What is injector impedance?
  • Can I fit larger injectors and expect my car to run correctly?
  • What is injector latency (deadtime)?
  • Are all injectors created equal?
  • Injector Sizing Chart

Why do you need larger injectors?

Factory injectors are selected to support the power output of a stock engine. While the factory almost always provide a little extra flow, if you are planning on a moderate increase in power, then chances are you will need to fit larger injectors to keep up. Don’t forget that the factory fuel pump will probably need to be replaced about the same time!

"What is injector impedance?"

There are two types of injector available – High impedance and low impedance. When you are upgrading your injectors it is important to choose the right type or you may end up damaging your ECU. You can tell which type of injector you have by measuring its resistance. A low impedance injector will measure 0.5-4 Ohm, while a high impedance injector will measure around 10-14 Ohm.

Can I fit larger injectors and expect my car to run correctly?

A swap to a larger injector will require tuning to get everything running right. If your new injectors are only marginally bigger, then the car will probably still start and run, but your mixtures are now likely to be too rich. At best this is going to hurt your power, but in worst case scenarios, it can lead to constant fouled spark plugs, and damage to your engine from bore-washing and fuel contamination of your oil.

What is injector latency (deadtime)?

An injector is a mechanical device and they don’t open and close instantly when the ECU signals them. There is a small delay from when the ECU opens the injector, until the magnetic coil actually lifts the pintile off the seat and fuel begins to flow. This small time is measured in milliseconds, and is called the injector dead time or latency.
An injector with a very short deadtime can respond faster and is more accurate. This is important to make your car idle properly if you fit larger injectors.

Are all injectors created equal?

No, there have been some huge improvements in injector technology recently, and the newer breed of injectors are able to operate faster, atomise fuel better, and are more linear in their operation.
This means that you can fit large injectors to your car without sacrificing idle quality and driveability. In general your car will be smoother to drive, will use less fuel and make more power with a modern injector design.

What you need to know:

If you need larger injectors for your car, here is what you need to know to choose the right injector the first time. If you still aren’t sure or have any questions we will be happy to help.
  1. Injector size -  Check the reference chart below, which shows how much power a single injector can support. Multiply this by the number of injectors fitted to your engine and match the injector size to your estimated engine power.     
  2. Injector style –  Injectors are available in side feed or top feed variants. You will need an injector that is compatible with your engine.     
  3. O-ring size –  Top feed injectors are available in either 11mm or 14mm diameter o-rings. Typically Japanese vehicles use 11mm, while US vehicles use 14mm.     
  4. Injector impedance –  Fitting the wrong impedance injector to your car can damage the ECU. To select the right injector you need to know the impedance of your factory injector.

Injector Sizing

See the chart below for an approximate guide to injector sizing:

Approximate Power Per Injector
Flywheel Power @85% Duty Cycle

Injector Size (cc/min)

Pump Fuel (kW)

E85 (kW)

*NOTE: The above chart is approximate only.