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Illustrated: A typical Injector
Illustrated: A typical Injector
Injectors: The fuel injector is a fancy name for an electric solenoid valve. It is a valve that when you apply electricity it will open and allow fuel to flow through. The catch is that it is a very precision valve. The injector must flow a precise amount at a specific pressure and be able to open and close very fast.

The ECM controls the injector turning it OFF and ON for different amounts of time depending on how much fuel the engine needs. There are several different shapes of injectors for different applications but they still work the same way. Some operate at different pressure ratings.
Illustrated:
Illustrated: An Injector Crossection
They range 12 to 20 PSI for most throttle body systems and 40 to 50 PSI for most port injection systems. Injectors have different electrical resistance. Throttle body injectors are usually 1.2 or 2.4 ohm and are considered Low impedance. Port injectors can be either 2.4 or 12-16 ohm with the 12-16 ohm injectors being considered high impedance.

High impedance injectors are general purpose and used in many production cars and are driven with what is called saturation drivers.
The Low impedance injectors are usually found in high performance injectors or injectors used on high RPM engines and require a Peak and Hold type of driver. High impedance injectors can be used on either type of driver, but Low Impedance injectors cannot be used on a Saturation driver.

Injectors also have a defined “spray” pattern. Most Throttle body injectors spray in a wide fan spray while a Port injector sprays a narrow pattern that is directed at the open valve. They can be interchanged but some performance may be sacrificed.

The last point about injectors is their flow rate. Different size injectors are needed for different engines. It is kind of like changing jets in a carburetor. Most production injectors are rated at 15 to 30 pounds of fuel per hour. This means that if the injector is open full time that it will actually flow this many pounds per hour of fuel. There are about 6 pounds of Gas per Gallon. Higher flow injectors are available for racing up to 200 lb./hr for alcohol racing applications. A rough rule of thumb is that you can get 2 HP for every lb./hr of fuel. This means if you have 8 20lb injectors then you have the ability to generate a maximum of 320 HP.
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