Size of Injectors depend on calculated fuel flow at full throttle on the fuel required. I use 8 injectors - 4x1700cc & 4x1000cc. The mapping will allow the car to pootle along if you require or run at full throttle with 1000bhp on a race fuel like FTW Purple that uses 60% more fuel than pump. A modern ECU can control these huge injectors with great accuracy. It does not mean bad fuel economy on light throttle if your mapper knows what he is doing. Have seen 22mpg on a long run on the Motorway dropping to 4mpg on a Topspeed run. The words chuck in loads of fuel has made me chuckle that's not what its about.