Why can small engines make high horsepower, but almost never high torque?

Question

So I am aware of the existence of high specific output engines like in the Honda S2000 or Ferraris, but one common criticism those cars tend to have is their lack of torque. Why does it seem so difficult for these engines to make more torque as well?

In: Engineering

Answer 1

Torque and horsepower are not two independent properties of an engine, they’re tied together via the RPM by a formula:

T = P * 9549 / r

Where T is torque in N*m, P is power in kW, and r is rotational speed in RPM. (for power in HP and torque in lb*ft the coefficient is 5252)

So if you have a 10 kW engine and connect it to a gearbox which outputs, say, 950 RPM, you will get around 100 N*m of torque regardless of the engine “size”.