Just a bit of technical info really, please feel free to correct me or add info.
A petrol injector will make approx 1 bhp per 5cc/min flow rate at a safe 80 percent maximum duty cycle and 3 bar fuel pressure. So if you consider a YB cosworth with 380cc injectors it will make 380/5 = 76bhp per cylinder, thats a max of 304bhp. It is possible, but not advisable to run more duty cycle to get a touch more. Its also possible to run a higher fuel pressure, but the realationship between pressure increase and injector flow rate is equal to the square route of the increase, twice as much pressure does not mean twice as much fuel, far from it.
I hope this will help anyone planning on upgrading or speccing injectors for a power output, after all you will not make 300bhp if you dont have the energy (or fuel) for that power figure.