I cant give you an exact answer, as everything varies due to engine type, but having helped rebuild a diesel train & two steam trains, I know that a typical diesel has as low as 200 horsepower, but has nearly 6 to 10 times that amount of torque at very low rpm. Because the engine itself has such a large internal displacement, the inertia & torque it puts out is massive, even at low rpm, because the weight of the reciprocating mass & the inertia of the crankshaft spinning is huge. Car engines on the other hand, have a comparatively light reciprocating mass, and therefore need to rev far higher than a train for example, to make torque. The larger capacity an engine is, the more torque it will likely make. Consider this; a 1.8L Honda engine will rev to 7000rpm to make maybe 250 ft-lb of torque, but the engine in a bulk cargo ship will only rev to 500-800 rpm, but will make thousands of ft-lbs of torque. The cargo ship doesnt need to rev to produce torque, because it has a larger capacity. Of course, the bore diameter VS the piston stroke is a factor which can change that- if an engine has a long stroke & small bore diameter, it will rev less, but make a lot of torque. If the bore diameter is large and the engine has a short piston stroke though, it will rev much more & make power & torque in its upper rpm. Hope that helps you a little.