| Simplifying things in this comment a fair amount, but... Extracting more power is, most commonly, a matter of burning more fuel, which requires more oxygen. This increases combustion chamber pressure, which drives the piston down with more force; that force is converted to rotational torque and ultimately drives the wheels harder, pushing the vehicle forward faster. More oxygen can be added in any number of ways; less restrictive intake/exhaust parts, larger valves, cams that are more optimized for whatever load/engine speed you want to produce peak power (or are more optimized for output than, say, economy or emissions), supercharger, turbocharger. Adding fuel is more straightforward: A higher capacity pump and/or bigger injectors/carbs. You can also switch to pistons that will compress the air/fuel charge more. This also increases combustion chamber pressure. You can also run the engine at a higher speed, which will often warrant different cams, stronger valve springs, etc. May also require bottom end uprated components that can handle that task (connecting rods, pistons, bearings, crankshaft). On the subject of bottom end components, depending on how much you increase cylinder pressure, you may need to upgrade those. You can also increase output power by reducing losses - a lighter flywheel is a common example with enthusiasts. Every single one of these involves a trade-off. A lighter flywheel impacts drivability; removing intake/exhaust restrictions and adding forced induction components will both make more noise; etc. |
These greater forces cause more stress to factory engine components, so generally at a certain level you will need to replace engine internals with uprated parts e.g. stronger rods and pistons.