Unlocking 400 Horsepower from Your Ford Focus ST: A Comprehensive Guide by Alex Forte'
The Ford Focus ST is a beloved hot hatch, celebrated for its engaging driving experience and potent turbocharged power. But what if you’re yearning for more power—specifically 400 horsepower? Achieving this level of performance is no small feat and requires a methodical approach to upgrading the stock components while understanding their limitations. This guide will take you through the entire process, from identifying stock parts’ limitations to selecting and installing the right upgrades.
Understanding the Stock Focus ST Setup 
The Ford Focus ST comes equipped with a 2.0-liter EcoBoost inline-4 engine that produces a factory-rated 252 horsepower and 270 lb-ft of torque. While this setup offers impressive performance for a stock vehicle, pushing it to 400 horsepower necessitates significant modifications. Let’s break down the key components and their limitations:
1. Turbocharger
- Stock Turbocharger: The factory turbo offers great low-end power that makes for an enjoyable driving experience and an excellent autocross vehicle, but it will struggle to reach even 300 horsepower. With bolt-on mods, tuning, and ethanol, most Focus STs will end up around 260-300 horsepower on the stock turbo.
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Upgrade Recommendation: To achieve 400 horsepower, you’ll need a larger turbocharger capable of supporting higher boost pressures and airflow. Consider upgrading to an aftermarket turbo such as the BNR 2867 or 3071. The ATP Kit using Garrett turbos is also a great option! These turbos offer improved spool characteristics and higher power potential.
2. Fuel System
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Stock Fuel System: The stock fuel system struggles to keep up past 340-380 horsepower with a bigger turbo. Your available octane (91/93) will also play a part in how far the stock fuel system will take you. Ensuring the fuel system can keep up and provide a healthy air-fuel ratio is crucial to the health of your motor. Remember—lean is mean!
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Upgrade Options: We have come to a fork in the road! It's time to upgrade your fuel system, and there are two main routes to choose from: upgrading your direct injection system or adding a port injection system. This might be one of the most significant parts of this article, and we hope this will help you make an informed decision on what works best for you.
First and foremost, unless you have an absurdly large turbo, you will struggle to push past 400 horsepower on pump gas; it’s simply limited by octane and poses a greater potential for pre-ignition. So regardless of which route you go, you will want ethanol to attain a reliable 400+ horsepower setup.
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Upgrading Your Direct Injection System: XDI makes an upgrade for the HPFP and injectors for this vehicle, which will allow you to run straight E85 and clear 400 horsepower while leaving lots of headroom. These parts can be controlled by the factory ECU, which keeps the tuning process simple. The HPFP & injector combo retails at $1,999 at the time of this article.
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Adding Port Injection: Also known as Auxiliary (AUX) fuel, Precision Raceworks makes a great port injection kit that currently costs $949. This kit includes an intake manifold spacer, Bosch injectors, fuel rail, fuel line, and a Split Second controller, which is not controlled by the factory ECU. It will enable your fuel system to run straight E85 and achieve 400 horsepower while leaving headroom. The port injection kit also helps keep your intake valves clean of carbon build-up, a common issue on this platform. The kit does require some simple wiring, so we always recommend professional installation for aftermarket parts!
3. Intercooler
- Stock Intercooler: The factory intercooler is designed to manage the heat generated at stock power levels and honestly struggles to do just that. This should be one of the first upgrades on a bone-stock Focus ST.
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Upgrade Recommendation: An upgraded front-mount intercooler, like those from CVFab or CP-E, is essential. These intercoolers offer increased cooling capacity and lower charge air temperatures, which help prevent heat soak and maintain performance.
4. Exhaust System
- Stock Exhaust System: The stock exhaust is restrictive, especially at higher power levels. It can cause backpressure, limiting the engine’s ability to expel exhaust gases efficiently.
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Upgrade Recommendation: A high-flow downpipe and cat-back exhaust system are necessary for your 400 horsepower goal. Opt for an aftermarket downpipe with a high-flow catalytic converter, coupled with a free-flowing cat-back exhaust to reduce backpressure and improve exhaust flow. Our preferred choice is a CVF Catted Downpipe paired with an AWE Touring Catback!
5. Engine Internals
- Stock Internals: The stock engine internals are designed to handle the factory output but may not be as reliable at 400 horsepower without potential risks. Routine maintenance and proper tuning will help keep your motor healthy around the 400 horsepower mark.
- Upgrade Recommendation: While some high-output setups can run on stock internals, for added reliability, consider forged pistons and rods. Brands like Manley offer forged internals that can handle increased power and boost pressures.
6. Clutch
- Stock Clutch: The stock clutch isn't terrible, but excessive power can lead to premature wear and failure.
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Upgrade Recommendation: If you are planning on sticking around the 400 horsepower mark, the Focus RS clutch upgrade kit we supply is a great option to support that power. If you want to push for a bit more, closer to 450+, we recommend something such as an ACT Sprung 6 puck or even an XClutch Twin Sprung Organic for the load. Stepping to a lightweight flywheel setup or a twin-disc clutch may slightly suffer in drivability, but this a common trade-off made when building a powerful setup.
7. Tuning
- Stock ECU Tune: The stock ECU is calibrated for factory power levels and will not be adequate for the conditions changed by performing these aftermarket modifications.
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Upgrade Recommendation: A custom ECU tune using a Cobb Accessport is essential to optimize fuel delivery, boost control, and overall engine performance. Work with a reputable tuner who can create a custom map that maximizes power while ensuring reliability and drivability. All of our in-house Focus STs are tuned by Ryan Martin at Engineered Motorsports Solutions!
8. Bypass Valve & Intercooler Piping
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Stock Diverter Valve & Intercooler Piping: One major difference between the OEM turbo on the Focus ST and aftermarket "big turbo" upgrades is that big turbo upgrades capable of 400 horsepower do not have the 3-bolt flange on the compressor housing for a factory-style bypass/blow-off valve. For this reason, upgrading to a big turbo will require you to implement a BOV elsewhere. For this platform, the solution is to mount a BOV on the cold side charge pipe.
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Upgrade Recommendation: There’s no need to custom fabricate a charge pipe with a flange to adapt an aftermarket BOV, because CVFab offers charge pipe options with BOV flanges. The two flange options are HKS (seated by snap ring) and Tial (seated using a clamp). Each flange needs to be paired with its respective BOV, so a Tial Q BOV will not work on an HKS-flanged charge pipe, and vice versa. These kits come with a block-off plate for the stock location if you choose to do this modification on the stock turbo prior to upgrading.
9. Air Intake System
- Stock Air Intake System: The stock intake on the Focus ST is quite good, and with just a high-flow filter, it can easily support enough flow for 400 horsepower. Larger turbo upgrades will feature a 3" inlet compared to the stock 2.5".
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Upgrade Recommendation: While it is possible to modify the factory intake, we recommend replacing it with an aftermarket full 3" intake to simplify the setup, enhance the engine bay aesthetics, and add some turbo noises. Injen is a great option for those not looking to break the bank, while CP-E is our fan favorite for overall looks and functionality! Be careful that early year models 13-14 and 15+ Focus STs require different intake kits.
Other Considerations
Any responsible owner modifying their Focus ST to reach 400 horsepower should acknowledge the importance of routine maintenance and account for conditions that will be more prevalent with a higher power setup. We highly encourage installing a catch can routed in the PCV system to help prevent excess blow-by from entering your intake system. We also recommend changing your oil more frequently and checking your spark plugs every time you change your oil. NGK 6510 spark plugs are always available from our store and will help ensure proper spark! Higher mileage vehicles should also consider intake valve cleaning and injector cleaning.
Final Thoughts
Reaching 400 horsepower with a Ford Focus ST requires a well-planned approach, focusing on upgrading key components to handle the increased power. By upgrading the turbocharger, fuel system, intercooler, exhaust, and ensuring proper tuning and supporting modifications, you can transform your Focus ST into a very quick car! Always prioritize reliability and safety alongside power to ensure an enjoyable and enduring driving experience.
If you have any questions regarding this topic, please don’t hesitate to reach out to us for more information relevant to your specific setup!