Ford Focus ST MK4 Induction & Cooling Upgrades

MK4 Focus ST induction and cooling buying guide

The 2.3 EcoBoost MK4 Focus ST responds extremely well to improved airflow and charge-air cooling, but you do not need to replace every part immediately when tuning the car.

The most important upgrades are the performance intake and intercooler. These form the basis of our Stage 1+ package and remain essential supporting hardware when moving to Stage 2.

Other products such as larger boost pipes, the top induction pipe and double front air feed are useful supporting modifications, but they are not mandatory for our normal tuning stages.

For expected power figures and the complete upgrade path, read our MK4 Focus ST tuning guide.

Does a Stage 1 MK4 Focus ST need an intake?

No.

Our Stage 1 calibration can be run on a completely standard car without changing the intake, intercooler or exhaust hardware.

However, a performance intake is still a worthwhile upgrade because it improves airflow into the turbocharger and gives the car a noticeably stronger induction sound.

In our experience, an intake can be worth approximately 5–10hp on a tuned car, depending on the complete specification and calibration.

Best intake for the MK4 Focus ST

We offer two main AIRTEC intake options:

• AIRTEC Motorsport Open Induction Kit
• AIRTEC Motorsport Enclosed Induction Kit

In our experience, the two systems perform very similarly.

The decision therefore comes down mainly to how much induction and turbo noise you want.

AIRTEC open versus enclosed induction kit

AIRTEC open induction kit

The open-cone system is the louder option.

You will hear considerably more:

• Turbo spool
• Induction noise
• Airflow under acceleration
• Turbo noises when lifting off the throttle

For owners who want the 2.3 EcoBoost to sound obviously modified, this is normally the one to choose.

AIRTEC enclosed induction kit

The enclosed system offers similar performance but keeps the induction noise more controlled.

It is still more noticeable than the factory intake, particularly on a tuned car, but it is noticeably quieter than the open-cone option.

This makes it a good choice for a daily-driven car where you want the airflow improvement without as much additional noise.

Does the open intake suffer from heat soak?

We would not choose between the two AIRTEC systems based purely on concerns about engine-bay heat.

In normal use, both are suitable for tuned cars and we see similar overall performance from them.

For the MK4 Focus ST, controlling charge-air temperature after the turbocharger with a good intercooler is considerably more important once the car is being pushed hard.

Does Stage 1 need an intercooler?

No, but we consider it a very worthwhile upgrade.

The factory intercooler is one of the major limitations on the MK4 Focus ST during repeated hard use.

Once the intercooler becomes heat-soaked, intake temperatures rise and the ECU can begin reducing performance to protect the engine.

This means the first hard acceleration may feel strong, but repeated pulls can become progressively less consistent.

Even on a Stage 1 car, fitting an uprated intercooler can make the performance much more repeatable.

When is the intercooler required?

For our tuning packages:

• Standard car: Not required.
• Stage 1: Optional but strongly worthwhile.
• Stage 1+: Required.
• Stage 2: Required.
• Track use: Strongly recommended regardless of tuning level.

AIRTEC MK4 Focus ST intercooler

The AIRTEC Motorsport MK4 Focus ST intercooler is our preferred charge-cooling upgrade for the car.

It uses a substantially larger stepped-core design to increase cooling capacity while still fitting behind the factory bumper.

The larger intercooler allows the car to maintain lower and more consistent charge temperatures during:

• Repeated acceleration
• Dyno pulls
• Fast-road driving
• Hot weather
• Track use

Does the larger intercooler increase turbo lag?

Not to any noticeable degree in our experience.

The improvement in charge-air temperature and repeatability considerably outweighs any theoretical increase in system volume.

The car still retains good turbo response while becoming much more consistent when driven hard.

Does the AIRTEC intercooler require trimming?

Yes, AIRTEC states that minor trimming is required during installation.

The intercooler fits behind the original bumper and connects to the original boost pipes if the standard pipework is retained.

The modification is relatively minor compared with the substantial increase in intercooler capacity.

Does the MK4 Focus ST need uprated boost pipes?

Not necessarily.

The AIRTEC Big Boost Pipe Kit is a worthwhile supporting modification, but it is not required for our normal Stage 1, Stage 1+ or Stage 2 tuning packages.

It replaces the approximately 2-inch standard boost pipework with 2.5-inch pipework.

The larger system provides a smoother, less restrictive route between the turbocharger, intercooler and engine.

When are 2.5-inch boost pipes worthwhile?

We would particularly consider them for:

• Stage 1+ cars where the owner wants to optimise the complete intake system
• Stage 2 cars
• Cars subjected to repeated hard driving
• Track cars
• Owners planning further upgrades later

They are a supporting modification rather than something you need to fit before the car can be tuned.

AIRTEC top induction pipe

The AIRTEC Top Induction Pipe replaces another section of the factory intake tract with freer-flowing pipework.

It is another useful supporting modification that improves the overall airflow route into the turbocharger.

However, it is not a mandatory component for any of our normal tuning stages.

We would normally prioritise:

1. Performance intake
2. Intercooler
3. Then additional intake and boost pipework

This gives the best return from your initial budget before optimising the smaller restrictions in the system.

AIRTEC double front air feed

The AIRTEC Double Front Air Feed increases the amount of outside air directed towards the intake system.

It is another useful supporting modification rather than a requirement for a particular tuning stage.

Its main benefit is helping maintain a good supply of cooler outside air during repeated hard use.

That can help improve consistency and repeatability during successive pulls, particularly when the vehicle is being driven hard or used on track.

Do I need the double air feed with an AIRTEC intake?

No.

Both the open and enclosed AIRTEC induction systems can be used without the double air feed.

Think of it as an additional optimisation rather than a prerequisite for fitting the intake.

MK4 Focus ST oil cooler

The AIRTEC Motorsport Oil Cooler Kit is aimed primarily at cars that experience sustained high engine load.

For a normal tuned road car, we would not consider an external oil cooler essential.

The factory cooling arrangement is generally sufficient for normal road driving, even when the car has been remapped.

When is an oil cooler worthwhile?

We would recommend considering one for:

• Track use
• Long high-speed sessions
• Repeated sustained hard driving
• Cars regularly experiencing high oil temperatures

A short road pull and a 20-minute track session place very different thermal demands on the engine.

For road use, spend your money on the intercooler first. For regular track use, additional oil cooling becomes much more valuable.

Forge atmospheric dump valve

The Forge Motorsport Atmospheric Dump Valve is primarily a sound modification.

Instead of recirculating the released boost pressure quietly through the intake system, it vents to atmosphere and produces a much more noticeable dump-valve sound when the throttle closes.

We would fit this mainly because the owner wants the additional noise rather than expecting a significant performance gain.

Forge recirculating valve

The Forge Motorsport Recirculating Valve keeps the quieter, more factory-style operating principle while providing an uprated valve design.

This is the better choice if you want a more robust aftermarket valve without the loud atmospheric release noise.

Does every tuned MK4 Focus ST need an uprated valve?

No.

If the original valve is working correctly, there is no need to replace it simply because the car has been remapped.

Consider an uprated valve if:

• The original valve has developed a fault
• You specifically want the atmospheric sound
• You want an uprated recirculating replacement
• You are upgrading the complete induction and boost system

Best upgrades by tuning stage

Standard MK4 Focus ST

No induction or cooling modifications are required.

Good optional first upgrades include:

• Open or enclosed AIRTEC intake
• Intercooler if the car is regularly driven hard

Stage 1 – 335–345bhp

No supporting induction or cooling hardware is required.

Our preferred optional upgrades are:

• AIRTEC intake
• AIRTEC intercooler for improved consistency

Stage 1+ – 360–370bhp

For our Stage 1+ setup, the key hardware is:

• AIRTEC open or enclosed performance intake
• AIRTEC uprated intercooler

The big boost pipes, top induction pipe and double air feed are all worthwhile additional modifications but are not required.

Stage 2 – 370–385bhp

Retain the Stage 1+ induction and cooling hardware:

• Performance intake
• Uprated intercooler

Then add the appropriate Stage 2 exhaust hardware and calibration.

At this level, the following become useful additional supporting upgrades:

• 2.5-inch big boost pipe kit
• Top induction pipe
• Double front air feed

Track or sustained hard use

For cars seeing regular track use, we would prioritise:

• Uprated intercooler
• AIRTEC oil cooler
• Performance intake
• 2.5-inch boost pipework
• Double front air feed

The emphasis here is not simply peak horsepower. Keeping temperatures controlled allows the car to deliver its performance repeatedly rather than only on the first pull.

Hatchback versus estate fitment

The induction and cooling parts in this collection use the same fitment across the MK4 Focus ST hatchback and estate.

There is no separate intake or intercooler required simply because the car is an estate.

Pre-facelift versus facelift

The induction and cooling upgrades covered here are suitable across MK4 Focus ST model years, including pre-facelift and facelift cars.

There is no separate performance intake or cooling upgrade path required for the facelift model.

Manual versus automatic

The induction and cooling fitment is also shared across gearbox variants.

The choice of manual or automatic transmission does not change the intake, intercooler or cooling recommendations in this guide.

Frequently asked questions

Does a Stage 1 MK4 Focus ST need an intake?

No. Stage 1 can be run on the standard intake, although a performance intake is a worthwhile upgrade.

How much power does an intake add?

In our experience, around 5–10hp is realistic on a correctly tuned car.

Open or enclosed AIRTEC intake?

Performance is very similar. Choose the open intake for considerably more induction and turbo noise, or the enclosed system for a quieter and more subtle setup.

Does Stage 1 need an intercooler?

No, but it is one of the most worthwhile supporting upgrades because it improves consistency during repeated hard use.

Does Stage 1+ need an intercooler?

Yes. Our Stage 1+ package requires an uprated intercooler and performance intake.

Does Stage 2 need an intercooler?

Yes. The Stage 2 setup retains the intake and intercooler required at Stage 1+.

Does a larger intercooler cause more turbo lag?

We have not noticed any meaningful increase in turbo lag from the AIRTEC intercooler.

Does the AIRTEC intercooler require cutting?

AIRTEC states that minor trimming is required to install it behind the original bumper.

Do I need the 2.5-inch boost pipes?

No. They are a useful supporting upgrade, particularly on Stage 1+ and Stage 2 cars, but are not mandatory.

What size are the AIRTEC boost pipes?

They increase the boost pipework from approximately 2 inches as standard to 2.5 inches.

Do I need the top induction pipe?

No. It is another worthwhile airflow improvement but is not required for any of our normal tuning stages.

Is the double front air feed required?

No. It is a useful supporting upgrade that helps supply cooler outside air and improve repeatability during hard use.

Does a tuned road car need an oil cooler?

Normally, no. We recommend the oil cooler primarily for track use and sustained hard driving.

What is the difference between the Forge atmospheric and recirculating valves?

The atmospheric valve produces considerably more dump-valve sound. The recirculating valve retains quieter, more factory-style operation.

Do I need an uprated valve when tuning the car?

No. A healthy standard valve can remain in place.

Do these parts fit the estate?

Yes. The induction and cooling parts covered here use the same fitment across hatchback and estate models.

Do they fit facelift cars?

Yes. The induction and cooling upgrade path is shared across the MK4 Focus ST generation.

Does gearbox type affect fitment?

No. The induction and cooling components covered here are suitable across the relevant gearbox variants.

MK4 Focus ST tuning guide

For Stage 1, Stage 1+ and Stage 2 power figures, required hardware and our complete tuning recommendations, read our MK4 Focus ST tuning guide.

More MK4 Focus ST performance parts

Browse our complete range of MK4 Focus ST performance parts for exhaust, clutch, braking, suspension, servicing and styling upgrades.