How to increase the horsepower on a Ford Focus?

I have a 2005 Ford Focus and I want to increase the horsepower. What are some good ways to do this and what kind of performance gains can I expect?

One of the best ways to increase horsepower on a Ford Focus is by installing a performance air intake. This will improve air flow to the engine, resulting in a noticeable increase in horsepower.

Another option is to install a performance exhaust system. This will not only increase horsepower, but also give your Ford Focus a more aggressive sound.

Upgrading the engine's tune can also lead to a significant increase in horsepower. Consider getting a custom tune or purchasing a programmer to adjust your engine's performance settings.