Just asking.....when an engine is dyno tested, why not run it as it will be run in the car, ie, alternator, water pump, power steering pump (if using), ac (if using)? That should give a real number, right?
It isn't very practical to hook all of that stuff up on the dyno. Besides, nobody really cares about the 10 or 15 hp that the accessories consume, that isn't the point of the dyno test.
