The internal combustion engine is an AIR PUMP.
More air in = more power out.
(as long as the fuel delivery system can keep up with the correct mix)
Cold air = more air
Turbo = more air
As for all the inexperienced want to be gear heads out there there is one book that will answer all your questions about how an internal combustion engine works at a easy to understand teaching level.
Even cover clutches throw-out bearings how and when to shift, wheel alignment.
[ame="http://www.amazon.com/Keep-Volkswagen-Alive-Step-Step/dp/1566913101"]How to Keep Your Volkswagen Alive: A Manual of Step-by-Step Procedures for the Compleat Idiot: John Muir, Tosh Gregg, Peter Aschwanden: 9781566913102: Amazon.com: Books[/ame]