Whats the difference in doing injectors VS doing delivery valves? both add more fuel correct? is there a difference in pressure or duration?

 

The injectors are the final metering orifice to the engine.. You can add all the fuel you want upstream with DV's or plates etc, but the injectors are only going to give you a max amount of flow. If you want full band increase in fuel, injectors are the ticket. DV's will help, don't get me wrong, but its all upstream of the final point to the engine.. FWIW..