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FAQ

How do I know what cc/lb Fuel injectors do I need? - Back To Top
A: Please click our fuel flow chart link at the top of the page, or Click Here

Do I need low impedance or high impedance injectors? - Back To Top
This depends on the driver signal that your ECU delivers to the injector. If you are using a OEM ECU ( even if it is “flashed”), you can measure the impedance (Impedance is the resistance measured over the terminals and also called the “Z”, as in “high Z” or “low Z”) of the OEM injectors and match the impedance category (high Z or low Z) that the OEM injector is. This is the simplest way to make sure you don’t damage your ECU. See “How do I know if my injector is low impedance or high impedance?” to determine what injectors you have. Many aftermarket ECUs are able to drive both low and high impedance injectors, but you need to contact the manufacturer of your ECU to determine your choices.

Typically most injectors with higher flow rates (1000cc/min or more) would be more likely to be low impedance injectors. This is because low impedance injectors have a faster opening response times and generate less heat when operated at higher flow duty cycles.


How do I know if my injector is low impedance or high impedance? - Back To Top
You can measure the resistance across the two terminals of the injector and if it is between 1.5 and 4.0 Ohm, you have a low impedance injector and if the range is between 10 and 16 Ohm you have a high impedance injector.


What are the differences between low impedance/peak & hold and high impedance/saturated injectors? - Back To Top
Low impedance injectors (1.5 to 4.0 Ohm) have a faster trigger times due to the type of electrical signal pattern emitted by the ECU. This “Peak and Hold” pattern uses a high (6 amp) initial current pulse to open the injector, and then a lower current signal to keep the injector open. Since the “hold” or lower current part of the signal has created a weaker magnetic field, the injector will also close quicker.

High impedance injectors (10 to 16 Ohm) are triggered by a low (1 amp) constant current signal and kept open by the same constant (saturated) current for the entire cycle. Due to the lower current needed, less heat is generated during each cycle allowing the injector to stay cool and therefore increase its reliability. The down side is that the trigger time is decreased since there is less of an initial current to actuate (open) the injector.

Most OEM injectors are saturated injectors since car manufacturers are most interested in reliability.


What is base fuel pressure? - Back To Top
Base fuel pressure can mean the pressure at which the injector flow rate is determined or the fuel pressure that a particular fuel system starts (idle pressure) at. When SFI flow its injectors, whether for flow matching or for cleaning services, we use the widely accepted pressure of 3 Bar (43.5psi) to compare the injectors. Since raising the fuel pressure raises the flow rate, it is important that the industry has a “base” pressure so that it is easy to compare injector flow rates. If you are not sure of the pressure that an injector was rated at, you need to find out, otherwise you may have a significantly larger or smaller injector than what you think. (Dodge Neon SRT-4 injectors use a 55psi base pressure, so their injectors would flow about 10% less at 43.5 psi.)


At what fuel pressure do you rate your fuel injectors? - Back To Top
All SFI injectors are rated at 3 Bar or 43.5 psi.


What difference does a spray pattern make? - Back To Top
In the performance world we are always looking for small improvements to increase output. In our case we choose the best spray pattern we can get for a particular application. Typically speaking, the wider or more diffused the spray pattern is , without spraying sideways against the manifold walls, the better the fuel will be atomized and the better the flame propagation (burn) in the cylinder. This is why our most popular injector is the Rochester type, which are well known for their wise spray patterns.

In some cases we are able to improve on the spray patterns as we customize our injectors, (See 1000cc vs 1050cc spray pattern.), but in some cases we must compromise the spray pattern to be able to offer injector flow sizes that would otherwise not be available. These compromised spray pattern still offer good full throttle characteristics while providing tenability at idle.


SFI 950cc (1000cc) vs SFI Custom 1050cc spray pattern - Back To Top

Spray Pattern for 950cc Injector Spray Pattern for 1050cc Injector
950cc Spray Pattern 1050cc / 1150cc spray pattern
Small cone angle Wider cone angle
Dense fuel stream Atomized fuel stream

Here at SFI we have developed many custom injectors and we have spent hours revising spray patterns on our custom injectors to provide you with the best injector possible. None have been more successful than our outstanding 1050cc and 1150 cc Rochester custom injectors. Check out these side by side pictures of the spray pattern of a regular 950cc/min injector and our 1050cc/1150cc high flow injectors. (The equivalent of our 950cc injector is also advertised elsewhere as a 980cc, 1000cc and as a 95lb/hr injector by other companies. Don’t be fooled, these are all based on the same injector.)


Will your injectors plug into my wiring harness? - Back To Top
The most common injector plug is the EV1 / Bosch style plug which is found on most Bosch, Siemens, Denso, Delphi, Lucas injectors from 1985 through 2005. This plug fits most of the injectors that SFI sells and it is the same plug that is the OEM plug on the Mitsubishi Eclipse and Evo harness.

It is always wise to check what the plug looks like on your wiring harness and compare it to the injectors you are purchasing. If your plugs do not match, it is a relatively easy fix. We sell all plug and play connectors according to your needs, Or pig-tail will fit your oem harness. SFI sells a variety of pig tails for the different applications.

There are certainly many other plugs styles that have been used by the different injector and car makers over the years, but if you are looking to customize your engine in stages, we advise that you switch to the EV1 plug, since it will fit the widest variety of after market injectors.