In terms of duration IN SECONDS on a PER CYCLE basis, at peak torque is where it will be longest (assuming you dont run massively rich AFRs just to one side of peak torque for some reason).

In terms of duty cycle as a percentage of elapsed time, it will be nominally at peak BHP

This is because although the fuel requirement drops off after peak torque, so to does the induction stroke timebase.


So basically, the injectors are flowing most at peak power, but open for longest each time they open and close at peak torque.
(assuming you dont max them of course!)