I know nothing (Sgt Schlutz) about the Renix system. So take it with a grain of salt.
But most speed density EFI systems inject fuel by how long they hold the injector nozzle open, called pulse width. So for a bigger injector with the same fuel pressure, you'd get more fuel for the same pulse width. You'd also get more fuel with the same injectors, but greater fuel pressure is another trick. BUT, most EFI system are adaptive, meaning they use the O2 sensor to "infer" how close you are to the stoichiometric 14.7:1, then they make adjustments to the pulse width to get the 14.7:1. It doesn't really read the A/F Ratio, the O2 sensor isn't that accurate, buts its very accurate at always crossing over right at 14.7:1, so the computer really tries to bounce back and forth just a little over and under the 14.7:1 to keep it really close to that figure. Usually the computer stores the adjustment and re-uses them when the same conditions come up later.
So if you put in bigger injectors, the computer will inject more fuel at first, but it will notice its rich and then make an adjustment and reduce the pulse width to get the same amount of fuel as before.
Now, in some conditions, the motor needs richer A/F than the 14.7:1. Like warm-up and Wide-Open-Throttle (WOT), and in those cases the O2 sensor can't help at all, because all it can do is tell you when you bouncing back and forth between just over and under 14.7:1. Thats OPEN LOOP Mode, meaning the Feedback Loop of the O2 sensor is now open and not providing any feedback. In Speed Density Systems, the computer just goes off a table of the spec engine needs for fuel in the conditions present and uses that pulse width. So in this case, at WOT and Warm-Up, bigger injectors would result in more fuel being injected. That is, if the Renix system is different than Chrysler and Others. Most systems also apply the correction table learned in normal CLOSED LOOP Mode to the OPEN LOOP MODE. So, if you put in bigger injectors, the computer notices and reduces pulse width to get the same amount fuel as before in all modes.
Besides, you get more power by getting MORE AIR AND FUELinto the motor, just adding fuel makes you go rich and if anything you lose power.
Sorry, but a CAT Back and Hi-Flow CAT is NOT enough to increase airflow thru the motor that you would need bigger injectors. Like mentioned before, bigger injectors would most likely just be a waste of money. Spend the money on something more likely to make power.
