Both RC Engineering and Deatschwerks offer detailed websites explaining how to select the proper injector size for the target horsepower you are aspiring to achieve. And if you're too lazy for manual calculations both offer an automatic calculator for injector sizing vs target horsepower. Note: for your injectors to function reliably please ensure your duty cycle is not over 75% at maximum load (RC states 80% as the danger point, Deatchwerks states 90% while Andrew says 75% from personal experience. You decide. Duty cycle is the amount of time the injectors remains open in relative to the amount of time it is closed. 0% means the injectors are not in use while 100% means the injectors are switched on or opened ALL the time.
RC's Fuel Injector Sizing Calculator
Deatschwerks Fuel Injector Sizing Calculator
And so what are the size of stock QG16 and QG18 injectors? The honest answer is I don't know. I've gone thru the service manuals for both N16 and B15 yet came up with nothing. Maybe I need to read in more detail? A search on the great big place in the Matrix - the Internet actually, revealed that stock QG18DE injectors could be 240cc. However one person claimed 180cc which frankly to my opinion is too small but one cannot imagine what TCM is capable of doing especially since the experience of knowing that they (TCM) fitted a puny gearbox to the N16 manual version. Guess I'll know once I dismantle and test flow the stock injectors.
I do know that for the power I'm aspring and my engine spec I will require 600cc to be on the cautious side. Those that have maxed out injectors till failure will know the very painful and expensive consequences. Have ordered Deatschwerks 600cc injectors which have been shipped as I type this.