The problem with using an electric motor is the rpm of the motor needs to be held at a fixed ratio to engine rpm If you want to use the stock pump with it's control valve to control fuel flow properly. If it's held at a constant rpm , at lower engine speeds or lower demand, it will have to bypass alot of fuel leading to heat . The bypass strategy and metering needs to be reconfigured for a constant rpm pump. A variable volume pump would be better for a constant rpm setup.
If you wanted to replace the current chain driven hpfp and run it with a motor, the hp needed to run the pump at a given rpm and pressure can be calculated using the hydraulic hp equation. But thats theoretical and doesn't take into account efficency of the pump and losses in the motor. Also keep in mind the duty cycle of the pump will affect the size of the motor. Ex. starter motors (decent power to weigth. But a very short duty cycle). The shaft hp needed to drive the stock pump at 3000 psi and enough flow for 320 hp is a little under 1.5 hp. Again not exact but just to give you an idea that's a little over 1.1kw. At 12v and 100 percent conversion to shaft hp from the motor ( not possible ) that's 93 amps. Take into account inefficiencies your well over 100 amps. The alternator would need to be upgraded for that load and the battery as well.
If it's a supplemental pump in parallel with with the stock one, the wattage needed to drive the pump is going to depend on alot more factors ( target hp, target rail pressure, duty cycle, efficiency, etc) . Either way alot of things need to be considered with an electric driven pump. You can start to see why mechanical drives have a serious advantage over electric when it comes to transfering energy. This is also why mechanical fuel pumps are almost necessary for large hp applications.
