Cubic capacity is the sum of the volumes of all the cylinders of an engine. eg. a 999 cc 3 cylinder engine has 3 cylinders of 333 cm^3 each.
Torque is the work that an engine is capable of doing at a certain rpm. Can also be expressed as the force that an engine can exert on the drivetrain or pulling power of the engine.
Power is the rate at which the engine can do work (As defined by torque). It is given by the work being done multiplied by the speed at which the work is being done. Power at any rpm = Torque at that rpm x Rpm (For Horsepower we divide this figure by 5252).
The ratio of torque produced to the engine displacement is determined by the compression ratio of the engine, which is the ratio of minimum and maximum volume of the cylinder (ie. When piston is at the top and bottom of it's travel respectively). Since diesel engines have use heat of compression to burn fuel, they need a much higher compression ratio (Around 17:1) than petrol engines (Around 10:1). Hence they typically produce more torque than petrols of equivalent size.
Since diesel engines cannot usually rev as fast as a petrol one due to slow burn rate, heavy internals, longer piston stroke, etc. they tend not to have a very high peak power figure. However, you will often find that in the lower rev range diesels would be producing more power than petrols. (Since rpm is constant but torque output is higher)
Turbochargers and Superchargers both use the engine (Exhaust gases and Drive belt, resp.) to run air compressors. This compressed air increases the pre-ignition pressure inside the cylinder, resulting in more torque (and hence power) output at that engine speed.
Large turbos compress air to a very high pressure, but need to be spinning extremely fast to do this, hence are only active at high engine speeds. This creates turbo lag.
Small turbos do not have have turbo lag, but can compress air less effectively, creating a less noticeable increase in engine output.
Variable Geometry turbochargers use different methods to change their internal volume. This means that they behave as a low-pressure (small) turbo at lower rpms, and a larger one as the engine gains revs. Result is no lag, and a lot of boost at the top end.
When engineers develop an engine, they do not just try to extract the highest output figures. Engines are designed to meet an immense range of criteria including Fuel efficiency, Reliability, Cost, Part sharing, NVH, etc.
A more realistic method to compare engine output is using the power and torque curves, as this shows the usability and delivery of output figures throughout the rev range.
