I always get asked questions about injectors to turbo. I tend to think a different way than an injector guy. Turbo guys(me) can never have enough air, into the combo, injector guys can't have enough fuel.
This all goes back to the basic fact of what a diesel engine wants, air. Diesel love air more than fuel, fuel makes big power in a diesel but also with high EGT's. You can have a truck with 205 stock injectors put down over 500rwhp, with right tune but egt's would be too high for horsepower to be used other than a few seconds on the dyno, or track.
On the other hand pump alot of air in and smallest amount of fuel to hit the right combo and you get big horsepower, just as much as the fuel but now it's usefull power. How much air to fuel easy, that's where the dyno helps, not so much as power output measure but to see horsepower to torque measurement.
For example:: if you are running a big turbo, with alot of flow( I like to start with air first), stock injectors,and put on dyno. Say you get 500rwhp, but torque is at 890lbs, and this is very important egt's are at 1000 degrees. Now you now that there is not enough fuel, due to egt and torque being too low for rwhp, should be just about even. you could try to increase fuel but then you might be max out so now increase the injectors. What to, not 175/75, injector but 155/35 first and then make your way up, from there. 155/35 might have you at 525rwhp and 1025lbs of tq and say egt's at 1250dregrees, that it you hit the limit of horsepower for that combo. Now if egt's where a little higher you could adjust timing a little lower through tune, but of course hoursepower and torque may go down alittle.
Some people have got a hold of me and say I got a deal from the injector guy on some 190/100, so what do I need turbo wise. I tell them flat out you didn't get a great deal, why? easy the turbo for 190/100 would be a stage 3, and with that much air and fuel you would be over 600rwhp easy. What's so bad about that, well now put money aside for tranny, because it will tear up a stock tranny. So 4500-6000 dollars for a transmission ,and the deal on injectors wasn't so good, unless you knew that before hand.
Most of the owners I talk to want a strong, fast, truck that can tow, well that's a 500-540 rwhp truck. So what combo is that 155 injectors with a stage 1,(or powermax), Hybrid, or stage 2. If more power needed than water/meth can be used, now this is if you want a do it all truck. There are other combos that I will be getting together as I get things going better and hopefully other members can put together to get the best towing and all around truck. As I put more turbos with more air flow then injectors size can increase and then step up to another combo, but anything greater than the combo just mention and transmission needs to be considered.
Sorry for going on and on but, I hope this helps everone, and of course this is my opinion, and what I have learned so far with the combos.