Steve or John input on injector impedance.

[MegasquirtCA]

Im planning on upgrading my injectors soon to get close to 300whp. Fortunatly I have a choice on which impedance to go with for injectors, as you can tell I have Megasquirt so I just let it know which if I have High or Low (requires tuning for low to prevent burn out).

Now I was curious for the power level Im shooting for will the impedance make a difference in performance? I've gotten mix answers that low (Peak and Hold) is oriented more torwards performance and High (Saturated) is oriented more torwards drivability/idle and easier to tune with.


I'm looking to get 550cc High Imp as its easier because I just set everything to max in Megatune. But do you think it would be best to go with low Imp?

To give a rundown on my setup:
CA18DET motor wasnt opened up but freshend up with new gaskets, pumps, etc etc. Compression 160psi in all 4 cylinders
Stock 370cc Top Feed Low Imp injectors
Megasquirt II V3.0 running code 2.36
Brand New Garrett GTi-R T28 .60 A/R Comp .86 A/R Turbine
3" Exhaust and Stock Cast Log Manifold.
FORD EDIS-4 Ignition
31x6x3 Intercooler with 2.5" openings and 2.5" piping.
NGK BKR6E plugs
Stock fuel pump (upgrading to walbro soon)

[MegasquirtCA]

up up and away. IF anyone asks why not PM them, this could be some great info for others.

[bardabe]

stick with low impidence that;s my opinion

[johngriff]

And you are right Juan.

Though the megasquirt has a "preference" to choose between Low Impedance and High Impedance, its control feature is almost moot. In this case the big differentiator between low and high impedance is the current draw they create. The ecu (whatever it may be) is simply a ground switch.

With that being said, and having a tunable platform (like the megasquirt etc) injector decisions are not based in the universe that the oem equipment will allow for.

High Impedance Injectors are wound more than Low Impedance injectors. The resistance of High Impedance injectors is much greater than low impedance, making the amp draw much less for high impedance, without using a resistor.

The down side to this, is this increases the Injector lag time of the solenoid, thus reducing minimum injector open time which effects idle in larger injectors, and effects the accuracy of these injectors at high RPM.

Low Impedance Injectors are deployed in this right. They are wound much less, yielding a lower resistance, but the solenoids are much faster, yielding a minimum injector open time MUCH lower than high impedance (.8ms vs 1.7ms typical). At idle with an 850cc, this can be 900 rpm or 1400 rpm. A drop resistor MUST be used with low impedance injectors. The resistor is to offset the lower resistance, and the resistor is placed on the supply voltage side of the injector, not on the ground lead to ecu.

The other differential that needs to be made is the advantages of a high quality injector like the RC injector or SARD injector. You will notice that the SARD injector body is much larger than your oem unit. The SARD (denso style II) uses a heavier duty solenoid and body. The yield is lower minimum injector times allowing for better idle control with larger injectors (such as the 550's you are eyeballing). Going with a 550 high impedance is going to leave you with some bad idle issues.

Hopefully that helps. In short.

Buy new SARD 550cc Top Feed Low Impedance, and you will be happier than a clam.