Well, Ed, I could explain this in terms of thermodynamic cycles of various engines, but some here might pooh-pooh the math and theory as being too airy-fairy for the discussion at hand.

In general terms, there is power in fuel in the form of heat. The job of any engine (steam, Otto/gasoline, diesel, Stirling, jet turbine, etc) is to extract as much of the power resulting from the ignition of the fuel as mechanical power. We do that by converting the heat and pressure of the burning fuel gas into mechanical energy. The more we allow the burning fuel gas to expand, the more pressure and heat we can extract from the fuel.

The "ideal" heat engine is described in thermodynamics by what is called the "Carnot Cycle" -- no engine can achieve the perfection modeled by the Carnot cycle, tho.

For a quick comparison of torques produced by engines without & with turbos, and the effect of stroke length, I'd recommend that people look at the Diesel Cycle modeling of an engine, then look at the Otto Cycle and then finally the Miller Cycle. For those who can work their way through the math, it becomes clear why diesels have more torque at a given RPM, and how stroke length corresponds to torque and efficiency.