Ford Focus RS MK2 Exhaust Systems & Downpipes

What is the best exhaust for the MK2 Focus RS?

Cobra Sport is our preferred exhaust brand for the MK2 Ford Focus RS.

The systems offer excellent quality, fitment and sound and are hand TIG-welded in the UK. The 2.5-litre five-cylinder engine also responds particularly well to an exhaust upgrade, so this is one car where we would happily recommend a complete turbo-back system even on a relatively mildly tuned road car.

Our favourite all-round setup is:

• Cobra Sport 3-inch downpipe
• Cobra Sport 3-inch sports cat
• Cobra Sport 3-inch non-resonated cat-back

Together, these components form a complete 3-inch turbo-back exhaust system.

MK2 Focus RS exhaust sound levels

The main decision with the cat-back system is how loud you want the car to be.

Resonated Cobra cat-back

The resonated version is only slightly louder than the standard Focus RS exhaust.

It retains a centre silencer, so it provides more five-cylinder character without making the car dramatically louder during everyday driving.

Non-resonated Cobra cat-back

The non-resonated version is noticeably louder than standard and is our personal preference for the MK2 Focus RS.

Removing the centre silencer allows much more of the five-cylinder exhaust note to come through while still retaining a conventional rear silencer.

The Cobra Sport MK2 Focus RS cat-back exhaust uses 3-inch pipework and is available in both resonated and non-resonated configurations.

Cobra Venom back-box delete

The Cobra Venom back-box-delete exhaust is a lot louder than the standard system.

It removes the conventional rear silencer and is aimed at owners who want an extremely aggressive exhaust note.

Cobra specifically lists the Venom system as a non-road-use product because it exceeds legal noise limits, so it should be treated as a motorsport or off-road option rather than a normal road exhaust.

Does a cat-back exhaust add power?

A cat-back exhaust is primarily a sound and appearance modification on the MK2 Focus RS.

You may see a couple of horsepower from the larger, less restrictive pipework, but the majority of the exhaust-related performance improvement comes from replacing the restrictive original downpipe and catalytic-converter section.

Choose a cat-back mainly for:

• More five-cylinder exhaust sound
• A different tailpipe appearance
• Larger 3-inch pipework
• Improved stainless-steel construction

Best exhaust setup for a tuned MK2 Focus RS

For a tuned Focus RS, our preferred setup is a complete 3-inch Cobra turbo-back system.

This consists of:

• Cobra Sport 3-inch downpipe
• Cobra Sport sports-cat section
• Cobra Sport non-resonated cat-back

This is a strong setup for standard-turbo and commonly tuned Focus RS builds and provides both the airflow improvement and the characteristic five-cylinder exhaust note most owners are looking for.

How much power does a turbo-back exhaust add?

On a suitably tuned MK2 Focus RS, we would expect a complete turbo-back exhaust to contribute approximately 10–15 bhp.

The exact improvement depends on:

• ECU calibration
• Turbocharger specification
• Boost pressure
• Intake and intercooler setup
• The exhaust system being replaced

The majority of this improvement comes from replacing the original downpipe and catalytic converter rather than the cat-back section alone.

Sports cat versus de-cat

Sports cat

A quality sports cat is our preferred option for a road-driven Focus RS.

The Cobra sports cat offers substantially improved flow compared with the restrictive original catalyst while retaining a catalytic converter.

At the power levels achieved by most tuned MK2 Focus RS builds, there is very little practical performance difference between a good sports cat and a de-cat.

A quality sports cat will flow almost as well while avoiding many of the disadvantages associated with completely removing the catalyst.

However, Cobra states that its sports catalyst is not EC homologated. It should therefore be treated as the more sensible road-use choice compared with a de-cat, but it does not guarantee road legality or an MOT pass.

De-cat

A de-cat removes the catalytic converter entirely and is intended for off-road or motorsport use only.

It will normally trigger an engine-management light because the ECU can detect that the expected catalytic-converter operation is missing.

A de-cat will not pass the required UK emissions test, and ECU software does not change its legal status for road use.

Is a de-cat more powerful than a sports cat?

There is very little meaningful performance difference at normal tuned Focus RS power levels.

A good quality sports cat flows extremely well, so we would not choose a de-cat for a road car simply in pursuit of a small theoretical airflow advantage.

For most owners:

• Road car: Sports cat.
• Off-road or motorsport car: Sports cat or de-cat depending on the build.

AIRTEC de-cat fitment

The AIRTEC Motorsport de-cat is a 3-inch motorsport component.

AIRTEC specifically states that this particular de-cat does not fit the standard MK2 Focus RS exhaust system and requires an aftermarket exhaust.

This is a product-specific fitment limitation, so do not assume that every aftermarket Focus RS front section will connect directly to the original cat-back.

The AIRTEC de-cat is sold for motorsport and off-road use only.

When is a 3.5-inch downpipe worthwhile?

The AIRTEC Motorsport 3.5-inch downpipe is aimed at owners who want to maximise exhaust flow beyond a conventional 3-inch setup.

We would consider it when:

• You are trying to extract maximum performance from the standard turbo.
• A hybrid turbo is fitted.
• A larger big-turbo setup is being built.
• You want additional exhaust-flow headroom for future upgrades.

For a normal tuned road car, a quality 3-inch Cobra setup is already an excellent solution.

The AIRTEC downpipe starts at 3.5 inches and reduces to a 3-inch flange so it can connect to a standard-size or aftermarket sports-cat section. AIRTEC also notes that the outlet can be modified for a larger exhaust configuration where required.

3-inch versus 3.5-inch downpipe

Choose a 3-inch downpipe if:

• The car has the standard turbo.
• The car is a typical road-focused tuned build.
• You want a straightforward complete Cobra turbo-back system.
• You are not chasing the absolute maximum airflow possible.

Choose the 3.5-inch AIRTEC downpipe if:

• You are pushing the standard turbo particularly hard.
• The car has a hybrid turbo.
• A substantially larger turbo is planned.
• Maximum exhaust flow is a priority.

Bigger is not automatically necessary. The correct downpipe should match the power target and the rest of the exhaust system.

Should the turbo-to-downpipe gasket be replaced?

Yes. We advise replacing the Genuine Ford turbo-to-downpipe gasket whenever the joint is disturbed.

The original gasket is exposed to substantial heat cycling and can deteriorate with age.

Reusing an older compressed gasket can result in an exhaust leak after the new downpipe has been installed, so replacing it while access is available is inexpensive preventative maintenance.

MK2 Focus RS exhaust fitment

The relevant exhaust fitment is the same across MK2 Focus RS model years.

The main compatibility points to check are the individual exhaust components rather than the year of the car.

In particular, check:

• Downpipe diameter
• Sports-cat or de-cat configuration
• Cat-back connection size
• Resonated or non-resonated option
• Whether a specialist part requires an aftermarket exhaust

Frequently asked questions

What is the best MK2 Focus RS exhaust?

Our preferred setup is a Cobra Sport 3-inch downpipe, sports cat and non-resonated cat-back.

Why do you recommend Cobra Sport?

We recommend Cobra for its build quality, fitment, sound and hand TIG-welded UK manufacture.

How loud is the resonated Cobra exhaust?

It is slightly louder than the standard Focus RS exhaust and is the more subtle option.

How loud is the non-resonated Cobra exhaust?

It is noticeably louder than standard and is our preferred setup for the MK2 RS.

How loud is the Cobra Venom exhaust?

It is considerably louder than standard. Cobra lists the system for non-road use because of its noise level.

Does a cat-back add much power?

No. Expect only a small gain. Most of the exhaust-related performance improvement comes from the downpipe and catalytic-converter section.

How much power can a full turbo-back add?

Approximately 10–15 bhp is a realistic contribution on a suitably tuned car.

Should I use a sports cat or de-cat?

We recommend a quality sports cat for a road-driven car. There is very little performance difference compared with a de-cat at normal power levels.

Will a de-cat bring on the engine-management light?

Normally, yes. Removing the catalyst commonly causes an emissions-related engine-management warning.

Will a de-cat pass an MOT emissions test?

No. De-cat components are intended for off-road or motorsport use only.

Does the AIRTEC de-cat fit the standard RS exhaust?

No. AIRTEC specifically states that its de-cat requires an aftermarket exhaust system.

When should I use a 3.5-inch downpipe?

It is most worthwhile when maximising standard-turbo performance or when using a hybrid or larger turbocharger.

Is a 3-inch turbo-back enough for most cars?

Yes. A complete quality 3-inch system is an excellent choice for the majority of tuned MK2 Focus RS road cars.

Should the turbo-to-downpipe gasket be replaced?

Yes. We advise fitting a new gasket whenever the downpipe connection has been disturbed.

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