Optimal Path to modifying your Focus ST250

Most owners of the Mk3 Focus ST come to a point where they want a little more from their car or are already part of the aftermarket world. This is your optimal modification guide when seeking maximum vehicle performance coupled with utmost reliability. 

Stage 1

Optimal Path to modifying your Focus ST250

Most customers start off with an intake system for their ST250. Besides the performance increase it also awakens the pleasing sound of air discharging or better known as dumping. The sound is increased by either fitting the COBB high flow filter or the Karter stage 1 or stage 2 intake kit. For software, we swear by the COBB Accessport v3. It is the most versatile tuning solution for the end user. This unit allows you to flash a new map to your vehicle (for your specific fuel), test your 0-100 and 1/4 mile times, troubleshoot any possible problems (error codes) and best of all have a live data display of pretty much every sensor on the car. The Accessport comes with Off the Shelf Maps (OTS Maps) from stage 1 up to stage 3. COBB Tuning also offers free updates to download as further development is made for this platform. 

Stage 2

The OEM intercooler is inefficient for anything other than stock performance of your Focus ST. With various options available, you will be spoilt for choice. The main function of the intercooler is to cool the charged air before it enters the engine. The cooler the air the denser it is and this creating more consistent power. This is a stepping stone to future mods. 

Stage 3

Due to emission restrictions for a globally sold vehicle, there is some sacrifice in exhaust gas flow which affects the vehicle performance. By changing the diameter of the exhaust we are able to maximise exhaust gas flow. The Karter downpipe can either be fitted with a high flow catalytic converter or as a catless system.

Stage 4

Here we start diving into the realm of much greater power. The OEM turbocharger is replaced with a unit of much greater flow thus allowing a higher volume of air to be pumped through the motor. Turbochargers are rated for different horsepower outputs, the higher the horsepower, the longer the turbo takes to spool (turbo lag). When reaching this stage, we recommend you discuss your needs with us so we can suggest the ideal set up. The OEM Fuel system will eventually reach its maximum efficiency and an auxiliary fuel system will need to be purchased.

At this stage, your vehicle has the potential to double its original power output. 

Stage 5

Stage 5 is all about meeting the customer’s requirements. At this level of power, the OEM engine components are not strong enough to withstand the additional cylinder pressure created. Depending on the customer’s needs and budget we will spec the parts accordingly to ensure maximum reliability. 


Following these guidelines, you will achieve maximum power. There are options in terms of alternative fuels such as higher octane fuel or running ethanol. We have catered for an ethanol OTS map up to stage 3. Please note that the above is a guide only and slight deviations can be made. If you are unsure, please contact us here.



The focus ST250 pre-facelifts have a relatively weak downpipe hanger bracket, this was strengthened with the facelift models but should be checked when fitting the Karter downpipe.