What are the best modifications for performance upgrades in a Ford Focus ST?

I recently purchased a Ford Focus ST and I am looking to upgrade its performance. What are the best modifications I should consider? I want to improve the power and handling capabilities of my car without sacrificing reliability.

As an experienced Ford Focus ST owner, I recommend starting with a high-flow air intake and a performance exhaust system. These upgrades will improve airflow and allow your engine to breathe easier, resulting in increased power and torque.

You should also consider upgrading your intercooler for better cooling and installing a cold-air or short-ram intake for even more power gains. Don't forget to tune your ECU to maximize the potential of these modifications.

To improve handling, invest in a high-quality set of coilovers and sway bars. These will reduce body roll and improve cornering capabilities. Additionally, upgrading to performance brakes will provide better stopping power and improve overall driving dynamics.