L28: 20 horsepower difference?

A bit benchracer in nature and also a bit useless as I don't intend to mod my car at all, but...

I've read in various places that the 280Z was nebulously "rated at 150 in 1975 and then at 170 horsepower in 1977" (usually with some specific note that the engine wasn't actually changed), in other places that all 280s have either 150 or 170, or etc...

But it seems like the 77's injection system was at least different in having lambda sensors if I'm not mistaken... could that account for the difference?

I'm sure this has been covered here before, but it's a rather hard subject to search for so What exactly ought to be the horsepower of any specific 280Z?