MoTeC M880 - Manual (Page 31)

MoTeC Installation 29
As a rule of thumb the engine will require about 5cc per minute per horse
power for petrol or gasoline. For alcohol a higher flow rate is required.
For example : A 600 hp V8 will require each injector to flow at least
600 hp x 5 cc/min/hp / 8 injectors = 600 x 5 / 8 = 275 cc/min.
Note that the flow rate of any particular injector is dependant on the fuel
pressure applied to it.
Sometimes oversize injectors are used to maintain lower duty cycles, since
high duty cycles reduce the effect of sequential injection, since the injectors
are turned on for most of the time. However this can affect idle fuelling as the
injector may have trouble delivering small amounts of fuel.
Flow Rate Matching
The flow rate of injectors can vary between injectors of the same type. It is
advisable to match the flow rates of injectors by testing each injector on a flow
bench.
Fuel Pressure
The fuel pressure applied to the injector will directly affect the amount of fuel
that the injector delivers. Doubling the pressure however only increases the
fuel flow by about 1.4 times.
Most injectors will only operate correctly over a certain range of fuel
pressures. If the pressure is too low then the fuel may not atomise properly. If
the pressure is too high then the injectors may not turn off fully. Many
injectors will operate correctly at 2.5 bar (29 psi) and some will operate up to
5 bar (73 psi).
Current
Different injectors require different operating currents. The ECU injector
drives must be programmed to suit the injector using the Injector Current
setup parameter.
Pulse Width
The amount of time that the injector spends open during each injection pulse
is called the Injector Pulse Width and is measured in milliseconds
(thousandths of a second), abbreviated as msec.
The injector pulse width is controlled by the ECU according to the ECUs
calibration data.