Awfully presumptiuous for you to say you know more about cars than anyone here, yet know nothing about displacement.
Displacement is the referring to the cubic inch/liter size of the engine.
If you Increase displacement you increase the amount of fuel that can be burned in each cycling of the motor.
Thereby increasing HP and Torque.
Also as the Chevrolet engineers used to say (tongue in cheek) "By drilling bigger holes in the block for bigger pistons, we save some weight too."
For example, a stock SR20DETT Nissan motor displaces 2.0 liters (approx 131 cubic inches) and makes 246 HP in the Stock S-15 Silvia.
Whereas the R26DETT engine in the Skyline displaces 2.6 liters (about 157 cubic inches) makes 280HP or more in its stock configuration.
Does that help at all?