Low Impedance- 1.7 to 3.0 ohms (Peak and Hold Driver/Injectors)

This type of injectors and drivers also are called current sensing or current limiting. They are more expensive and complex than saturated circuit drivers, and are not generally used with domestic production ECUs. They are primarily used in aftermarket high performance systems. Most high flow injectors are low resistance (2-5 ohms) and use a peak and hold driver to activate them. The Peak current is the amount required to quickly open, and then the lower Hold current rating is used to keep it open for as long as the ECU commands. These require the extra higher current to keep the opening and closing time of the injector stable at the higher fuel flow rate. With this type of driver, 12 volts is still delivered to the injector, but due to the its low resistance, the current in the driver circuit is high. .

High Impedance- 10 to 16 ohms (Saturated Circuit Drivers/Injectors)

This Type Of Injector Is Used In Most Domestic OE production EFI systems.They use an ECU with 12 volt Saturated Circuit drivers. These are very inexpensive, simple, and reliable. This type of driver works by supplying 12 volts to the injectors and the ECU turns it on and off to establish a fuel injector pulse. In general, if an injector has a high resistance specification (12-16 ohms) the ECU uses a 12 volt saturated circuit driver to control it. This keeps the driver and injector circuit stays low keeping the components cool for long life.  Saturated Circuit drivers has a slower response time and closing time than a peak and hold type.

An injector operating on a saturated circuit driver typically has a reaction time of 2 milliseconds while a peak and hold driver typically responds in 1.5 ms.

 Manufacturers have used both types at one time or another.  The  way to determine impedance is to use a digital ohmmeter across the two electrical connections and see what it reads. The primary advantage of low impedance injectors is a shorter triggering time. When large injectors are fitted to high output engines, low impedance injectors will often give a better idle quality. The primary advantage of high impedance injectors is that less heat is generated in the drive circuit and often no external resistors are used

Nozzle Types

1) Pintle    2) Disc    

 3) Lucas      4) Ball           

1) This is the most common type and still the best. A tapered needle sits on a tapered seat. When the solenoid is energized, the core and needle is pulled back, allowing the fuel to discharge. This design has been well proven for over 30 years.

2) The Bosch disc type uses the same type of actuation mechanism as the pintle type but replaces the pintle with a flat disc and a plate with tiny holes. These work fine with a good spray pattern but are slightly more prone to deposits plugging the holes

3) The Lucas type buries the disc up inside the body to reduce the mass of the assembly for quicker response. The Lucas types typically have a very narrow spray pattern which can affect idle and throttle response in some cases.

4) The Rochester division of GM makes the ball type injector for OE applications as well as the larger flow race types for MSD. These use a ball and socket arrangement. These have excellent atomization and a wide spray pattern but are also prone to partial plugging by varnish deposits.

How much power is injector good for? That depends on the air/fuel ratio that is used, divide flow figure by 5 to get a hp capability.  322cc divided by 5 = 64hp maximum fuel flow with this injector.  Dividing the cc per minute figure by 10.5. For this injector, that gives a mass flow of 30.6 pounds/hour. To convert from pounds/hour to horsepower capability, multiply the figure by 2.04. So 30.6 pounds/hour multiplied by 2.04 gives a horsepower capability of 62.4hp 

Most OE injectors have low flow rates because stock power outputs are usually quite low on production engines and metering is more precise with small injectors for better idle and emissions. Very few production engines use an injector flowing more than 500cc/minute or 50lbs./hr. For performance applications, engines often require much larger injectors to satisfy the increase in fuel flow. Often larger OE injectors can be fitted from a different engine. Most systems maintain a fuel pressure of between 30 and 43.5 psi over the intake manifold pressure. Fuel pressure can be raised to increase the rate of fuel flow but this should not exceed 60 psi.