This article is by a writer at Precision Turbo...
but applies to any make of injectors
Precision injectors have fueled everything from daily drivers to today’s quickest and fastest race vehicles. These highly precise injectors range in domestic sizes range from 24 lbs/hr to 165 lbs/hr or 240cc to 1,600cc in high & low impedance configurations with a variety of nozzle styles. Flow matched and hand selected for optimal performance, Precision injectors are what you need for a wide variety of Domestic and Sport Compact engine applications.
Precision offers a variety of injectors to suit your needs. Many injectors utilize ball on cone sealing to for the most accurate fuel delivery possible. Test results have proven accurate metering in extreme conditions and underhood operating temperature ranges. Metering is controlled by a 6-hole orifice just below the valve which merges the fuel streams into finely atomized spray cone for improved starting and improved hot fuel handling. Each injector also contains an internal filter for increased protection against harmful fuel contaminants. Most Precision injectors are compatible with alcohol fuels and have low noise operation.
Fuel injectors provided through Precision go through a battery of tests to ensure accurate fuel delivery and reliability. Functional measurements that Precision audits include open/closing time, coil inductance, coil resistance, external leakage, static & dynamic minimum operating voltage, linear & dynamic flow, insulation resistance, response time, repeatability, slope & offset, impedance and voltage offset.
Unlike mechanical fuel injectors which run open constantly, electronic fuel injectors use timed delivery techniques by rapidly opening and closing. When injectors open, fuel pressure forces fuel through a tiny orifice and into the airflow coming through the intake runner. This action causes the fuel to break down into smaller droplets or a mist which is then carried to the combustion chamber. The amount of flow from an injector is determined by fuel pressure, nozzle size and duty cycle. Cleanliness of the injector tip can also affect the amount of flow, since a clogged injector can impede the delivery of fuel.
How much fuel is delivered is controlled not only by fuel pressure, but also by how long the injector is energized by the driver circuit in the vehicle’s ECU. This commonly referred to as duty cycle.
Injectors that pulse or open and close rapidly are measured in terms of milliseconds and have a variable duty cycle. Flow ratings for injectors are usually measured when they are in a static condition, which means they are held open continuously. This is referred to as a 100% duty cycle. In high performance applications, most injectors operate best when they are run at a 70 to 90% duty cycle, which means they flow 70 to 90% of the static flow rating. Operating an injector within this range helps reduce the build up of heat within the windings of the injector, which can lead to premature failure.
The volume of fuel delivered also depends on the amount of pressure within the fuel delivery system. Lower pressure causes less fuel to be delivered while higher pressure results in more fuel delivery. The advertised static flow rates are tested at a fuel pressure of 43.5 psi or 3 Bar.
Users should also remember that the use of larger injectors can also stretch the limits of a fuel delivery system. Always match the size of the fuel pump, line size and rail to the size and number of injectors installed. Contact Precision Turbo for information and best pricing on sizing your fuel delivery system correctly.
Since a vehicle’s ECM is the driving force behind the operation of an injector, matching injector impedance to the driver circuits within that engine management system is important. Mis-matching driver circuits with injectors can affect the reliability of the ECM and injector timing at high rpm ranges.
Injectors can also be categorized by their resistance to the electromagnetic force which opens the coil contained within the body. This resistance is also known as impedance and is measured in ohms. High impedance injectors are rated at 12 to 16 ohms while low impedance injectors usually have a resistance of 2 to 5 ohms.
Driver circuits are usually characterized as being either saturation or peak & hold, depending on how they operate. Saturation drivers are commonly found on OEM production vehicles because of their low cost and simplicity. These drivers use relatively low amounts of current and generate less heat, but also have a slower response time.
Peak and hold (also known as current sensing or current limiting) drivers are used more commonly on high flow, low impedance injectors and use a burst of power to open the injector quickly and then reduce the current to hold it open until the metering event is finished. Most peak and hold drivers will operate injectors of any impedance, but high flow, low impedance injectors should never be used with high impedance, saturated drivers.