Awesome Aussie Farming Ingenuity

Outstanding exercise and it sure looks mean, but 400 horses is quite pedestrian compared what's available over the counter and commonly in use.

Yeah but there's two of them.

BHP (Brake Horsepower) is a calculated figure - thus:
Brake horsepower = Torque (in foot-lb) x rpm/5252

So, I'm guessing that it wouldn't be revving above about 2,500 rpm

Substituting values
400 brake horsepower = (X x 2500) / 5252

X = (5252 x 400) / 2500
Therefore torque = 840.32 ft-lb

Even more pedestrian than I first thought. Most garden variety prime movers out there on the roads pulling 2 or more trailers are producing well over 2,000 ft-lb of torque. I don't want detract from the bloke's ingenuity, but it's no impressive power house in anyone's language.

Tractor pulls are great fun.