Changing from High imp to low imp injectors

[Deltona]

Hello all,

I'm going to have to change the petrol injectors on my car for some bigger ones due to a power increase, the problem is my car runs High impedance/high resistance injectors and the only ones I can find to replace them are low impedance ones and these will not work with my existing system. I have heard that you can upgrade your system by the fitting of 'ballast resistors' in the injector wiring.

Does anyone have any idea if this is possible and if it is, exactly how this can be done?

Thanks.

 

[reidh]

You need to determine the impedance of your current injector. It is probably in the 10-15 ohm range. The low impedance injector is likely under 5 ohm.

Add the appropriate ballast resistor so that the system impedance is the same with the low impedance injector as your original injector. Just make sure the ballast resistor is rated for the power you will be using.

Reidh

 

[Deltona]

Sorry, my post should have been more precise.
The original high imp injectors are 14.5 ohm and the new ones are .5 ohm.
Also, the original injectors (supplied with the car from the factory) are rated at 6 - 16vdc.

Soooo:

I will need a resistor of 14 ohm which will handle 16 volts right? Presumably I can go some way over this voltage, but by how much? 24v be ok?
Also presumably the resistor will need placing in the +tive side of the injector drive wiring and one per injector?

Sorry for all my questions, but thanks for the reply!

 

[NormPeterson]

It's not just the voltage or resistance that you're concerned with. Reidh has already mentioned
"Just make sure the ballast resistor is rated for the power you will be using."

So a 14 ohm, 1/4-watt resistor is probably not going to work for very long. I think you may also want to spend a little time thinking about how (and perhaps where) you're going to dump the heat that a resistor of adequate power rating will generate, though.

Norm

 

[bub579]

The Nissan 280Z has a setup which you have desribed. It bolts on to a inner fender panel. Nice setup, never seen one go bad. It had a heat sink and shield around it. Good luck

 

[dgallup]

I seriously doubt your new injectors are 0.5 ohm, I have never seen an injector that low. 2.0 to 2.5 ohms is typical for a low impedance multi-point injector. Typical ballast resistors are 6 ohm, 5 watt power resistors. You need one for each injector wired in series with the injector. This gives you a slightly greater current draw than your stock setup but your drive circuit should be able to handle it. You can also have your stock drive circuit drive a peak & hold drive circuit which eliminates the need for ballast resistors but will cost more.

 

[reidh]

Good point Norm. It would be probably be best to mount the ballast resistor on an aluminum plate, in an area that gets air flow.

.5 ohm does sound low for an injector. You may want to double check that.

Reidh

 

[bigpaul]

Stick with hi impedance injectors what size are you
looking to use cc or lbs per hour

 

[bradrs]

Will those 0.5 ohm injectors properly open with that low of a current though? For worst case calcs there, assume you have a low voltage(during cranking or similar condition) of 8-10V. With 14.5 Ohms total resistance, you are going to have a 0.6A, give or take. I would suspect that would be a problem for a low impedance injector. They use higher current to operate normally.

You need to determine current requirements of the injectors, and current drive capability of your ECU. If its not adequate, a peak hold circuit like dgallup suggested might be worth investigating. Or just find better suited injectors.

 

[Deltona]

Hello all,
First of all thanks for all your replies - makes interesting reading.
Things have moved on a bit since my initial ideas/post on the subject and I have learned more, some inline with your ideas, some not, i'll pass it on regardless...
The car is a modified 4 cylinder 2 ltr turbo motor and I'm hoping for 350bhp max when the ECU is remapped.

The injectors I had in mind were Bosch 0 280 150 403 'Greys' Picked because they should supply enough fuel for the power output expected and are readily available here in the UK. The resistance I was quoted was indeed wrong, they are 2.5 ohm I borrowed one and checked it with my tester.
The idea of using seperate resistors in series will cause injector lag so no good. Apparently you can get a separate peak-and-hold injector driver box for these type of applications which would work better.
Even better again of course is to use the correct resistance injectors in the first place so I am searching for an injector of standard Bosch motorsport style/size, which will supply enough fuel for my power output, I am suggesting a 550 cc High imp saturated injector.
Any help/ideas welcome.
Thanks.

 

[bradrs]

Depending on a few things, you may want to go larger than 550. Does your ECU support this easily? I know for the Denso injectors on the Mitsubishi 2.0 turbos I am most familiar with, 550, 660, 720cc are all pretty common size, and can be had in the same resistance and connector as stock so that they are basically drop in replacements. A larger than needed injector would give you some overhead to account for different fuels, increased power demand, etc. You just need to make sure your ECU is capable of fine enough resolution that it will still idle acceptably.

Depending on what you are looking for, there might even be some factory injectors are large enough to meet your goals.

 

[bigpaul]

High use Siemens 675cc they are high impedance and they are great at small duty cycles they make gray injectors look pre historic

 

[dgallup]

"The idea of using seperate resistors in series will cause injector lag so no good."

Not true if you use 6 ohm resistors. Many vehicles used to come from the factory that way back when high impedance injectors were strictly low flow weaklings. I have measured the better dynamic range with a ballasted drive setup than a peak & hold driver or high impedance injectors.

 

[bigpaul]

Clibration on low impeadance injectors at high duty cycles
is poor and influenced buy voltage change,injector offset
is also difficault to set accurately and as a consequence
when using large injectors at low duty cycles it becomes
a balancing act to keep it in tune over any peroid of time.
Despit compensation tables in the ECU.