What is the best engine upgrade for the Ford Fiesta ST?

I recently purchased a Ford Fiesta ST and want to upgrade the engine for better performance. I've heard of several different options, such as a cold air intake, turbo upgrade, and ECU tune. Which one would give me the biggest bang for my buck and how much horsepower can I expect to gain? Is there anything else I should consider? Thanks in advance for any advice!

I have a friend who has a Ford Fiesta ST and he recently upgraded his turbo. He saw a significant increase in horsepower and torque, and he also noticed better throttle response. I would recommend looking into a turbo upgrade, just make sure you do your research and get a reputable brand.

Personally, I would go with an ECU tune. It's a more cost-effective option compared to other upgrades and can give you a significant power boost. Just make sure you find a reputable tuner who knows the ins and outs of the Fiesta ST engine.

I would suggest starting with a cold air intake. It's a relatively easy and affordable upgrade that can give you a noticeable improvement in horsepower and engine sound. It's a good starting point before moving onto more expensive upgrades.