The old AEM wouldn't support my injectors without a $350 dollar box, the guy tuning the car said he could use the resistor and work fine. I never did the research into why it worked. I think we were at about 40% duty cycle. The new system will be able to run them or I won't get it. Thanks for the info!
It will work, but "fine" is questionable. It is probably OK at high duty with most injectors. You are making a good choice to avoid that nonsense.
Let's assume you have 5 ohm injectors and 14.5 volt battery. A typical saturated transistor would drop about .8 volts over a wide range of current, so you have 14.5-.8 = 13.7 to deal with.
I'm just going to make up numbers. Let's say the injector is 5 ohms, and the wiring loop resistance .5 ohms, and your tuner uses a 4.7 ohm resistor to get up closer to the 10-15 ohms of a hi-Z injector.
Add the resistances:
.5+ 5+ 4.7 = 10.2 ohms
Divide available voltage by total resistance:
13.7/10.2 = 1.34 amps
Now multiply that answer, 1.34, times any resistance and you have the voltage across that component.
1.34 * 5 = 6.7 volts
You are running the injector on 6.7 volts.
What this does is slow the injector opening significantly, speed the injector closing slightly, and make the injector more sensitive to voltage supply, temperature, and pressure changes.
Running injectors on reduced voltage at opening, which is what the resistor does, is stupid. A proper circuit would apply full voltage to snap the injector open smartly, and then fold back to a reduced hold current, then do a normal release. It costs about 50 bucks in parts and materials to do that, so it would probably cost a few hundred out the door from a manufacturer.