There is no such thing as a "fuel to air ratio" when talking about a diesel. A diesel should always have an excess of air, with fuel-rate determining engine speed/power/emissions. A turbocharger just allows more fuel to be injected, to make more power.
Most fuel injection pumps use a #5 resistor. The resistor is used to calibrate the fuel-rate of the injection pump. Due to mechanical tolerances, some pumps need a little more help than others, which explains the need for a calibrating resistor. Can't go wrong with a #5.