injector sizing and impedence??

[fe66comet]

I was looking at injectors today as I am moving forward with my fuel system since my parts came in for the rest of the plumbing and cell. I see there is a lot of variables involved as far as impedance , flow rate and pressure. I have a fuel pump rated to 80 psi and a regulator rated for high or low pressure. I would think ultimately I would fall in at 35-40 psi on a ford injector? correct me if I am wrong? At this pressure what size and impedance injector should I be using with ford power train modual at roughly 550-600 hp as you guys suggested my engine may produce. Considering I am going port injection and using an 80 mm throttle body rated at 1150 cfm@ WOT. Thanks....Jon

[Joe-JDC]

That information should be readily available from the supplier of your system of choice.  Joe-JDC

[fe66comet]

I am building my own system using a mass air flow system using a trick flow Cleveland intake and one of Jays adapters.

[fe66comet]

It appears after some research 42LBHR will be about right @ 40 psi and 85% duty cycle. I still haven't. Found a sound explanation of resistance, it looks like I have three choices 12,12.4 or 11-13 and saturated circuit or not.what's the difference it makes I have not a clue??

[jayb]

I have Ford 80 pound injectors on my SOHC and run them at 45 psi; I think that is about standard for most EFI systems.  Relative to impedance, the injectors can be roughly classified into two groups:  High impedance and low impedance.  Low impedance (peak and hold) injectors are in the 2 to 4 Ohm range, and high impedance (saturated) injectors are in the 10-15 Ohm range.  The link below explains the differences:

http://www.enginebasics.com/Engine%20Basics%20Root%20Folder/Fuel%20Injectors%202.html

[fe66comet]

Thank Jay

[BigNate]

In case you are looking for There are a number of very good old injector tech threads on the old "turbomustangs" site (now turboforums.com after the wonderful liars... errr... lawyers... in Ford's trademark office made them rename)...  Look in the DIY section.  "Back in the day" there was a VERY strong technical core membership there.  I've not been on that forum much in the last few years and I understand that it has changed a bunch since the old days - but that all the old threads are still there - and I remember some very lengthy / detailed discussions about the relative merits of low vs high impedance injectors as well plenty of threads on fuel system sizing / design. 

[fe66comet]

I was looking at some mustang sites'  info before but a lot of it seems to be conflicting and very lengthy. I suppose I could contact Moats when I order my Quarterhorse and see what they say. Thing is my CID far exceeds that of any small block and the application lookup for a modified Mustang includes many options. From the article Jay sent there are advantages to a peak hold injector over saturated circuit but at my power level I do not think any real gains would be seen.

[jayb]

One advantage to the high impedance injectors is that a lot of the EFI units (like the MS3X that I run) can drive them directly in a full sequential mode.  The MS3X is not able to drive the low impedance injectors that way, making individual cylinder tuning impossible unless you run an external resistor box, which basically converts the low impedance injectors to high impedance injectors.

[fe66comet]

I saw converters were available for the Fox body up PCM and the Fast EMCM, at what point does it give a gain? I know you are pushing big numbers so it would be a justifiable amount even at a small percentage. In your opinion  would I realize any benefits? I would be nice to have the ability to set individual lean/ rich settings for each cylinder. I think the Moetes tuner has the capability with a software upgrade.

[My427stang]

Don't waste your time and money on low impedance (Also referred to as Low Z) injectors for your application.  Really the only benefit, assuming your injector driver is able to control it, which it isn't without add ons, is during low injector duty cycle times, they react quicker.  Think modern car emissions not hot rod performance.  However, with your current plan, you aren't going to run a wide band O2 sensor anyway, so it will never need to do that.   We are also talking EPA type adjustments, not fine tuning.  It'll still tune to a knife edge.

With that being said, if you needed 80 lb or greater injectors, the pattern starts to get sloppy at low duty cycles, but I haven't heard of that until you get real big

So as far as sizing recommend you go bigger never smaller than the calcs give you (within reason) and shoot for a 80% duty cycle.  I get 39 lbs for a 500 hp motor which I would round up to 42 for pure gas, if E85, I'd go at least 50 lbs, and based on that, with the blends out there now at the pump, I would be most comfortable with a 45 lb injector

[fe66comet]

Thanks, it looked like I was in the 40-50 range but was thinking a 42lb injector but I will step up to a 45. Is some brands better than others, or are they all essentially the same?