... but every injector has its limit, like when you get to 100% duty cycle, the only other thing is to up the fuel pressure.

There is a rough way of calculating injector size needed. Maybe someone can search and find, or even write it themselves. There is a cirtain amount of petrol needed per kw of power (assuming fuel ratios and efficiency of the motor you have). Once you have this number, then it's easy to calculate the injector size if you know your final power output, and the max duty cycle you want to run the injectors.

No numbers sorry... someone else can do the work.