I asked a technician a question about the relationship of BHP and lbs/ft and was told that horse power is a calculation of an engines torque production at a certain RPM.
The calculation is (lbsft x RPM) / 5252. Thus an engine making 300lbs/ft @ say 3000rpm (300X3000/5252) is producing 171 horses and subsequently 300lbs/ft at 6500rpm is making just over 371 horses.
At a Dyno they measure the torque and then the horsepower is calculated and put on the screen as well and this is why the lines cross at 5252rpm.
The logic apparently being that the longer the engine builds torque in the rev range the more horsepower it will produce but this can be at the cost of low end grunt and idle because it isn't possible to build torque over the whole rev range.
Is this all correct?? I'm just a bloke with a much loved scooby with the urge to spend money on her.