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How to Choose The Right Fuel Injectors

Nothing will have your engine running rough faster than the wrong choice of fuel injectors. Not only that, you risk ruining your engine altogether if you make the wrong decision. So it’s important to understand the factors you need to consider when deciding which fuel injectors are right for your setup.

Bigger is not always better
It’s easy to fall into the trap of thinking that bigger fuel injectors equal more power, but unless your engine is set up to deal with the extra fuel, you’ll be on a fast track to trouble. The excess fuel will flood the engine and it either won’t run at all, or will be running too rich. This can lead to fouled spark plugs and damage to the engine.

There is a whole range of things you can do to increase your fuel capacity to accommodate bigger fuel injectors but the main ones are:
- increasing the airflow – this can be done by installing a turbocharger or supercharger, or fitting a bigger throttle body
- installing a bigger exhaust
- remapping the computer
- fitting a bigger fuel pump
- adding an adjustable fuel pressure regulator.

Running too lean
At the other end of the scale is where you’ve modified the engine but the injectors aren’t delivering enough fuel to keep up. If you’ve added a turbo, a higher flowing fuel pump, a bigger exhaust and remapped your computer, you’re going to need bigger fuel injectors. Otherwise your car will be running too lean and you’ll have a situation where your it is sluggish and lacking in power at best, or at worst, you’ll burn out the pistons and destroy the motor.

Size does matter
Both of these scenarios highlight why it’s important to have the right-sized fuel injectors. The best place to start to work out the right fuel injector size for your needs is to get an understanding of how much horsepower you expect to achieve with your modifications. We recommend you enlist the aid of a reputable car tuner to determine this.

The other critical factors are:
- whether the car is turbocharged or supercharged, and
- whether you are using E85 or standard pump petrol.

Once these factors have been established, you can use the charts below to help you select the correct injector. The following considerations should be taken into account when using these sizing charts: horsepower is at the engine (you lose roughly 30 percent if calculating from the wheels); injector duty cycle is 80 percent; and fuel pressure is 43.5 psi (3 bar).

1. Injectors online fuel injector size chart - petrol and turbo

2. Injectors Online fuel injector size chart - petrol natural

3. Injectors Online fuel injector size chart - e85 turbo

4. Injectors Online fuel injector size chart - e85 natural

Fuel injectors are either high or low impedance. This refers to the measure of electrical resistance of the coil that drives the injector. A low impedance injector will have a resistance of 1-5 ohms, while a high impedance injector will have a resistance of 10-16 ohms. High impedance injectors will work fine in a car set up for low impedance but there is an exception. A few cars (like some Skylines) have a resistor running to the injector loom that must be bypassed if you are fitting high impedance injectors. You cannot fit low impedance injectors into a car set up for high impedance. This can damage the injectors, wiring harness or the car’s engine control unit (ECU). If you are unsure of which type of injector you have, your car tuner will be able to tell you.

Feed style and configuration
Other factors to consider in making sure you choose the right fuel injectors are the length (o-ring to o-ring) and diameter (top o-ring). Length ranges from 40mm to 65mm, while diameter of the top o-ring will either be 11mm or 14mm. Injectors are also available in side feed (also known as galley feed) variants so it’s important to choose a configuration that is compatible with your engine. Side feed injectors, as the name suggests, are fed through the side of the injector. This style of fuel injector is popular in some older Japanese cars.

Developments in modern fuel injectors
Fuel injectors have come along way in recent times, with the new breed operating faster and having much finer atomisation than their predecessors. In practical terms, this means that you can fit larger injectors to your car without sacrificing idle quality and smoothness, and your car will have higher performance using less fuel.

Note: This article has been written as a general guide only. Injectors Online recommends that you check with a reputable car tuner to make sure you have selected the right fuel injectors prior to making your purchase. Injectors Online will not accept refunds if you have chosen the incorrect injector size and they have been fitted to the car.

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