If you have the original paperwork from the original 42.5 injectors, they have a lot of info on them that tells you what you use to set the numbers to even from injector to injector, so injector offsets can be used, however, that said, it's not mission critical and suddenly impossible to tune in the new injectors without this info.
In the "old days" I was tuning with PowrTuners and had great experiences using basic math to help me get the proper numbers into the IFR (injector Flow Rate) table. Scanning later on with HPTuners backed up what I already new... that at least on my car and in my case, it was bloody near perfect in terms of a solution.
Let me explain why and then move on to the way this is done in the HPTuners.
I had been tuning my GTP well before the change to 42.5 lb injectors and the fueling part was pretty much perfection with the exception that when I installed the 3.2 pulley, the injectors went static at WOT above 5000 RPM.
Changing the injectors increased the fuel flow in a uniformed manner from idle to up top and for the car to run properly, IN THEORY I would need to lower the amount of fuel used and the extra headroom of the high flowing injectors meant that they never hit the wall and went static... which after changing that one table, is exactly what happened. What also happened is that my entire tune stayed as "locked in" as before I changed the injectors, which supported the methodology as being the correct one.
So, what did I do? Basic math.
42.5 divided by 36 = 1.18055
This obviously means that I increased fuel amounts by ~ 18% by installing these injectors.
In the PowrTuner program, I *lowered* the IFR tables uniformly by 18% and the car's tune came right back into line as if I had done nothing at all... except that I had an increased capacity of fuel available up top (18% more, to be exact!). I went from going static, to not being anywhere near static.
The entire rest of the tune (except for the very top end) remained identical.
Now, the HPTuner app works a bit differently than the now defunct PowrTuner and instead of telling it to reduce flow by a percentage, you need to tell it that at any given kpA value, that it is flowing MORE fuel flow, and therefore, it reduces the amount appropriately.
So, how is this done? Well, a few years ago, I made this small video that shows how.
Enjoy.
http://syner-g.no-ip.biz/GTP/_custom...injectors.html