Ways to add power are done in a few ways, but to do this you need to better understand how an engine works. First off the engine can be looked at like a big pump. It sucks in air through the intake, and then blows it out the exhaust. The air that is sucked in is also compressed with fuel in it and also ignited. We will call this Suck, Squish, Bang, and Blow.

SUCK: The art of getting more air into the engine there for allowing more fuel and making more horsepower.

Forced Induction: The art of cramming air into engine to raise the pressure above standard atmospheric levels.

Turbochargers: An exhaust driven air pump that forces air into your engine.
Superchargers: Supercharges Also known as blowers force air into your engine by compressing air much in the same way as a turbocharger, but instead of letting the exhaust spin the CHRA it uses a pulley connected to the crankshaft pulley.

SQUISH: The Compression stroke on a four stroke engine.
Ok there isn't very much you can do to improve the squish of your engine.

BANG: The act of combustion.

BLOW: The act of expelling spent fuel and air.

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Thanks.