Mk2 Ford Focus ST225 Engine Tuning (Complete Guide)
Updated: Feb 8
✔ This article has been fact checked.
The Mk2 Ford Focus ST (2005-2010) comes as standard with 225hp. The Volvo 2.5L 5 cylinder engine found under the bonnet is a capable engine with lots of power potential.
There are usually 4 stages of tuning for an ST225:
Each tuning stage requires a different set of modifications and upgrades to reach the power output listed.
In this article, we will explain what modifications it takes to achieve certain power levels with the Mk2 Focus ST225 and the power you can expect at each stage of tuning.
Stage 1 (~260-275hp)
A stage 1 upgrade is usually as simple as a remap. It'll usually provide around 260-275hp and 360-380 ft-Ib of torque.
Some tuning companies and manufacturers recommend installing a couple of extra mods for provide a better result, including the following mods.
Performance air filter (typically a foam filter)
Induction kit
De-cat exhaust
While these modifications are not required for a stage 1 tune, they will enhance the results, allowing your Ford Focus ST to be closer to the upper end of the range (around of 275hp).
It's also advised to upgrade your clutch since the clutches on the ST225 are prone to failing when tuned.
Note: When de-catting your car, it will not pass it's MOT as it will fail emissions testing, making it illegal on the road, it will also be slightly louder. Also, a decat exhaust may be required for pop and bang maps.
Stage 2 (~300-320hp)
Tuning your Focus ST225 to stage 2 will require some additional modifications, such as the following. The modifications below are usually required to see 320hp and around 420 ft-lb of torque on the Mk2 Focus STs'.
Performance air filter (typical a foam filter)
Induction kit
De-cat exhaust
3-inch exhaust system (cat-back and down pipe)
Larger intercooler
While you could get away with not installing a de-cat or down pipe, it'll limit the power output and you'll likely only reach around the 300hp mark on a stage 2 tune.
Stage 2+ (320-340hp)
A stage 2+ (oftentimes called stage 3) tune on the mk2 Focus ST will typically see a maximum of around 340hp.
At about 320hp, the fuel system is the limiting factor and needs upgrading to see a higher power output.
To reach the maximum power of the stock KO4 turbocharger you will need the following modifications on your ST225.
Upgraded wastegate actuator (Turbosmart IWG75 unit)
Ford Focus RS 440cc or 550cc fuel injectors
The upgraded actuator has a stiffer spring, allowing it to handle a higher boost pressure without opening the wastegate. You may notice a drop in boost pressure and power at high rpms without upgrading the wastegate actuator.
340hp seems to be the limit of the stock turbocharger on the Mk2 Focus ST.
Stage 3 (340hp+)
Stage 3 is also sometimes referred to as a stage 4 tune depending on the tuning company and manufacturer. It's usually what comes next after you've maxed out the stock turbocharger and need to upgrade to a larger hybrid turbo.
There are a few types of st225 turbocharger upgrades:
Custom
Hybrid
Big
A custom turbocharger is when the original turbo is modified and upgraded, this usually involves porting the housing, fitting a larger turbine or compressor wheel, and several other modifications.
A hybrid turbo is nearly the same as a custom turbo, but it usually offered as a mass-produced unit (such as the Pumaspeed X48 or hybrid Focus RS turbo).
A big turbo is an off-the-shelf turbocharger unit which is mass produced and can be installed on any vehicle, usually custom exhaust manifolds and intake piping are required to install one of these turbos to a Mk2 Focus ST225.
The power level of a stage 3 st225 can be anywhere over 340hp. I've seen some examples of Focus STs' running well over 600hp or even more on big turbo setups.
Additional Modifications
Other modifications could be added to optimise and possibly increase the power level a little bit more, including those listed below.
Upgraded camshafts: Higher lift and duration camshafts allow extra air to enter the combustion chamber and allow more exhaust gas to flow, improving power across a specific rpm range.
Cylinder head porting and polishing. Porting and polishing the cylinder head increases the diameter of the intake and exhaust ports of the engines head, improving flow.
Tubular exhaust manifolds. An exhaust manifold is usually cast and unequal in length, making a tubular exhaust manifold improves flow and exhaust scavenging, increasing power.
External wastegates. An external wastegate is usually installed with a big turbo and has extra benefits for power and adjustability.
Custom exhausts (3.5-4 inch exhaust systems and screamer pipe setups). With more power a larger exhaust is needed. Custom exhaust pipes can improve flow and power.
Bigger boost pipes. Larger boost pipes can enhance the flow of intake and compressed air, allowing better flow and top-end power.
Larger intercooler. A larger intercooler is usually required when the power increases to lower heat-soak and reduce intake air temperature.
Water/methanol injection system. Water/methanol injection increases octane rating of the fuel mixture, reduces intake air temperature and increases power potential of the engine.
Intercooler water spray kit. An intercooler water sprayer sprays cold water onto the intercooler, increasing the rate of heat dissipation, reducing intake air temperature.
There are many different modifications and tuning options for the Focus St225.
Maximum Safe Power on a Stock Engine
The Ford Focus ST225 engine is a popular platform for tuning due to its robust design and responsive turbocharged 2.5L inline-five engine.
In its stock form, the engine is capable of handling power outputs of about 380 horsepower, anything above this level will require forged pistons and connecting rods.
There are some common issues when tuning this engine, such as the following.
Pistons and Connecting Rods
It's important to consider the strength of the pistons and connecting rods when tuning the Ford Focus ST225 engine. These components are subjected to high stress and can fail if not adequately reinforced.
To ensure reliability and longevity, it is recommended to upgrade to aftermarket pistons and connecting rods made of high-strength materials.
Cylinder Liners Cracking
One potential issue to consider when tuning the Ford Focus ST225 engine is cylinder liner cracking. This occurs when the engine is subjected to excessive stress and heat, causing the cylinder liners to crack.
This can cause a loss of compression and a decrease in engine performance. To prevent this issue, it is recommended to upgrade to aftermarket cylinder liners made of high-strength materials.
There's a common preventative modification known as the "block mod" that can be done, it's essentially a small metal shim between the cylinder liners, adding strength. It's not fully understood if the block mod actually helps to prevent a cracked liner, though.
Clutch
Another important aspect to consider when tuning the Ford Focus ST225 engine is the clutch. As power output increases, the stock clutch may become overwhelmed and slip, causing a loss of power transfer to the wheels.
To address this, it is recommended to upgrade to an aftermarket clutch that can handle the increased torque produced by the engine.
Driveshafts
The driveshafts are a common issue with these Focus ST225s, they are prone to snapping, warping, and becoming unbalanced when tuned to higher power levels.
To overcome this issue, upgraded driveshafts such as Dreamscience S10 driveshafts or even replacing with genuine Ford driveshafts can solve this issue.