Not only do the bolt on parts have to 'match' each other, they have to be fine tuned to maximize your POTENTIAL. Many people bolt on parts and figure out their POTENTIAL horspower on paper. All are disappointed when they make their initial dyno run.
It takes more than just bolting on parts to make hp/torque.
As an example, read the dyno article I wrote for Kitcar Magazine
http://www.kitcarmag.com/techarticles/142_0401_dyno/
Roscoe