What mods? Up to 300+ FWHP the stock injectors and computer tune is pretty good. A little tweeking of the fuel pressure by using the SOP dyno will do fine for engines in this power range.
Power adders use more fuel, and may need some seriously big injectors. Pretty much everyone else beyond the 300 FWHP mark can trim WOT A/F by fuel pressure and using 24lb injectors & calibrated MAF.
Theoretical ideal a/f is 13.2-13.5:1 for max power in a NA application but every motor will be different. My 331 made max power at 12.8:1, many variables go into this cam and heads are two big ones.
As mentioned the computer has a set a/f ratio programmed in so unless you can modify program don't worry about it.