I am quite sure there is a formula for that, but I have not seen it. The Paxton SC kit uses the stock injectors and just over-runs them with up to 100PSI of fuel pressure. (using dual in-line booster pumps) Without a doubt the stock Viper injectors can handle that on a daily basis as Paxton/Vortech have never released a kit that does not go through TONS of reliability tests.
The way the NX kit can do such incredible numbers is based on a different way of adding fuel. Where the Paxton kit adds fuel pressure to the stock injectors, the NX kit taps into the fuel system and essentially adds two more fuel injectors. Originally the NX kit was limited to 300HP settings, but in depth research on their end and real world and dyno testing on our end resulted in the 450HP kit being released.
Lastly, motors that use a modified 'fuel return' system, which essentially is a larger pump and manifold mods for return lines, can handle 725BHP (so far) with stock injectors. This is with keeping the stock injectors and just tuning the AF with the fuel pressure. The limit to this method has not been reached by us yet. Our dry sump 725R car has no problem during high load runs with this configuration. Additionally, at the last SORC 1 mile shootout, this particular cars fuel system also supported an NX kit without lean issues.
I guess bottom line is stock injectors can produce suprising results when backed by the right system.
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Happy Holidays Gang!