What is a downpipe and which type to choose (guide)

On a turbo engine the downpipe is the first section of exhaust for the turbo and at the same time the most restricted part of the factory system. That is why most tuners do this upgrade right after a software remap, and often together with it.

In this guide we explain what a downpipe is, what it really brings, the three types available and how to choose between decat, a sports catalytic converter and the approved version. The prices come from our range, where we currently have more than 600 downpipe and GPF delete kits for VAG, BMW, Ford, Hyundai, Mini, Mercedes and others.

TC VAG downpipe for 1.8/2.0 TSI: 3-piece stainless steel design with a flex section, lambda bung and clamp

What is a downpipe and where does it sit in the exhaust?

The downpipe is the pipe connecting the turbo outlet to the mid section of the exhaust. The exhaust gases pass through it immediately after driving the turbine wheel. This is where the temperature is highest and every restriction in the pipe slows the turbo the most.

The factory downpipe has a narrow diameter, sharp bends and a built-in primary catalytic converter. On newer petrol engines (Euro 6d, from roughly model year 2018 onwards) there is also a GPF or OPF particulate filter after the catalytic converter. All of that reduces flow and creates back pressure the turbo has to work against.

A performance downpipe has a larger diameter (usually 3″, i.e. 76 mm), smooth transitions, stainless steel and, instead of the factory catalytic converter, either nothing, a sports cat or an approved sports cat. These are also the three types we describe below.

What does a downpipe bring in practice?

Less back pressure: gases leave the engine faster and the turbo spins more freely.
Faster turbo response (spool): you reach full boost a few hundred rpm earlier and the car feels livelier low down.
More power and torque: a downpipe on its own, without a remap, brings little. The real effect comes with a Stage 2 software calibration designed around the downpipe. On the 2.0 TSI or BMW B58 the downpipe is exactly the part that separates Stage 1 from Stage 2.
A different sound: a deeper, rawer tone. With the decat version it is also noticeably louder, with pops on overrun.
Lower exhaust gas temperatures: useful on track, where the engine runs at full load for long periods.

Important: with a decat and with most sports cats the engine warning light will come on without a software adjustment (fault P0420). The rear lambda sensor no longer sees the catalytic converter it expects. A remap fixes this and at the same time makes use of the extra flow.

Which three types of downpipe are there?

You choose a downpipe mainly by what replaces the factory catalytic converter inside it. That determines the price, the power, the sound and whether the thing is road legal at all.

1. Downpipe without a catalytic converter (decat)

An empty pipe with no catalytic converter at all. The most flow, the loudest sound, the lowest price. It is intended solely for track use and is marked by every manufacturer as motorsport only.

Advantages: the biggest gain in power and torque, the fastest turbo response, the lowest price.
Disadvantages: is not legal for road use, fails the technical inspection (emissions), requires a software adjustment, exhaust smell at low revs.
Price in our shop: from 188 € for TA Technix (in stock) up to around €800 for Milltek. For more powerful models such as the RS3, up to €1.500.

Examples from our range: TC VAG downpipe for 1.8/2.0 TSI (Golf VII GTI, A3 8V, Leon 5F, Octavia 5E; inox, 3″, with lambda sensor port, 379 €), TC B58 downpipe for BMW (299 €), TA Technix downpipe for Golf VII / A3 8V / Leon (261 €) and Milltek decat for Golf 7 and 7.5 (804 €).

2. Downpipe with a sports catalytic converter (200 or 300 cpsi)

It has a high-flow catalytic converter with 200 or 300 cells per square inch (cpsi). The factory one has 400 to 600 and more, so a sports cat keeps most of the flow while still containing some of the emissions and smell. The sound is more civilised than with a decat.

Advantages: almost the same power gain as a decat, more suitable for everyday driving, less smell and fewer pops.
Disadvantages: without approval documents it is still not road legal, and the technical inspection remains a risk. The price is higher because of the catalytic converter, and a software adjustment is also advisable.
Price in our shop: from around €780 to €2.700, depending on model and brand.

Examples from our range: Wagner Tuning 200 cpsi for VAG 1.8/2.0 TSI (1.020 €), Wagner Tuning 200 cpsi for BMW N55 (910 €), Milltek with a sports catalytic converter for Leon and Golf 7 (776 €) and Scorpion 5″ with a sports catalytic converter for BMW F20/F22 (998 €).

3. Approved downpipe with ECE certification (HJS)

A sports catalytic converter with paperwork. Milltek HJS ECE downpipe uses a catalytic converter from the German manufacturer HJS and has ECE approval. This is the only version you can have entered in the vehicle documents and take through the technical inspection without worry.

Advantages: legal road use once registered, no trouble at the technical inspection, with the quality and flow of a sports cat.
Disadvantages: the highest price, available only for a limited range of models, slightly less power gain than a decat.
Price in our shop: from €1.485 to €3.598.

We currently have 20 kits, among them for Audi S3 8Y, TT and Cupro Formentor (3.312 €), BMW G20/G21/G42 (2.227 €), Ford Focus MK3, Hyundai i30 N, Mini F56, Toyota Yaris and Seat Leon. You will find them all using the filter TÜV certificate: YES in the downpipe kits category.

What about a GPF/OPF delete on newer cars?

On petrol engines from roughly 2018 onwards there is also a particulate filter (GPF or OPF) after the catalytic converter. It is even more restrictive than the catalytic converter itself, so on these cars the downpipe often replaces both parts. Such kits are marked in our range as GPF Delete and, like a decat, they are for track use only.

Examples: Scorpion GPF delete for Golf R 7.5 and S3 8V (836 €), GPF delete for Hyundai i30 N (€165, with a before/after video) and TC downpipe for EA888 Gen4 (Golf 8 GTI, Leon 4, Formentor; 379 €).

If you want to stay legal on such a car, leave the filter in place and sort the sound with a GPF-back system, which replaces the exhaust from the filter back.

Will a downpipe pass the technical inspection?

The short, honest answer: a decat no, a sports cat without documents no, an ECE-approved one yes, but only after it is officially entered in the vehicle documents. A certificate in the glovebox is not enough. We described the whole procedure, what TÜV and ECE marks mean and where the entry is made, in the guide to type approval for performance exhausts in Slovenia.

Every product in the shop clearly states whether it comes with documentation for road use. If you are not sure, write to us before ordering.

How to choose the right downpipe for your car?

Check the engine code and drivetrain. The same model can have different turbos and different flanges. Downpipe for front-wheel drive often does not fit the 4MOTION or xDrive version.
Decide where you will drive the car. Track only: a decat. Daily road use and you want to stay legal: ECE approved. In between: a sports cat, with the risk at the technical inspection.
Check whether your car has a GPF/OPF. If it does, you need a kit designed for that version.
Match the diameter to the rest of the exhaust. Most downpipes are 3″ and connect to the factory or cat-back system connects via a 2.5″ or 3″ fitting. Check what is in the kit: clamps, gaskets, adapter.
Check the details. The flex section relieves the exhaust as the engine moves, and the connection for lambda sensor must be in the right place, and the material should be stainless steel.
Plan the software calibration at the same time. A downpipe and a remap belong together. Without a remap you will have a warning light for engine and only a fraction of the gain.

The fastest way to the right part is via the page for your car, which shows only the products that fit: VW Golf VII, Audi A3 8V, Seat Leon 5F, BMW 3 F30. For other models use the vehicle selector at the top of the page.

What else to upgrade along with the downpipe?

Intercooler: more flow means more heat. Larger intercooler keeps the power even after a few laps or a long pull.
Intake side: turbo inlet and a performance air filter open the path for air into the turbo, and the downpipe out of it.
Charge pipe: on the BMW N55 and B58 the factory plastic pipe tends to crack at higher boost. Aluminium charge pipe kit is cheap insurance.
Cat-back or GPF-back: for sound and looks from the catalytic converter or filter back. See cat-back systems or GPF-back systems.
Heat wrap: the downpipe heats everything around it. Exhaust heat wrap protects hoses, cables and plastics in the engine bay.

Which downpipe brands do we stock?

Milltek Sport (more than 300 kits): a British brand with the widest choice for VAG, BMW, Audi RS and Mercedes-AMG. Decat, sports cat and the only one with ECE-approved HJS downpipes.
Scorpion (more than 160 kits): British exhausts with a strong sound, decat and sports cat, plus GPF deletes for the Golf R, RS3 and M2. No approval, for track use.
TA Technix (almost 90 kits): the most affordable decat downpipes, in stock, for older VAG, BMW, Opel, Ford and Mazda models.
Wagner Tuning: German downpipes with a 200 or 300 cpsi catalytic converter for VAG, BMW, Audi S4/S5 and Honda Civic.
TC downpipe: our own stainless steel decat downpipes for VAG 1.8/2.0 TSI, EA888 Gen4, BMW N55 and B58, plus DPF delete pipes for VAG TDI and BMW M57. The best balance of price and build quality for a Stage 2 build.

Frequently asked questions about downpipes

Is a downpipe worth it without a remap?

No. On its own a downpipe brings little power, and the warning light for and with a decat and most sports cats the engine light will almost certainly come on. It is the Stage 2 remap that turns the extra flow into power and at the same time adapts the lambda sensor monitoring.

How much power does a downpipe bring?

It depends on the engine and the remap. On modern 2.0 TSI and BMW B58 engines the downpipe is exactly the prerequisite for a Stage 2 remap, which compared with Stage 1 brings a few dozen more horsepower and noticeably more mid-range torque. The exact figures will come from the tuner who writes the map.

Is a downpipe louder?

A decat does, noticeably, and adds pops on overrun. A sports cat deepens the sound but does not make it much louder. An approved HJS downpipe is closest to the factory part in volume, as it has to stay within the permitted limits.

What is the difference between a downpipe and a cat-back system?

The downpipe is the section from the turbo to the catalytic converter (or including it), while cat-back is everything from the catalytic converter back: mid silencer, rear silencer and tips. A cat-back mainly affects sound and looks, while a downpipe affects power. Together they make up a complete performance exhaust.

How long does fitting a downpipe take?

In a workshop usually 2 to 4 hours, depending on access to the turbo and how many factory bolts have rusted. On engines where the turbo is jammed against the firewall (a transverse VAG, for example), expect the upper end of that range. The software calibration follows the installation.

Conclusion

The downpipe is the single most effective exhaust upgrade on a turbo engine and the foundation of every Stage 2 build. For track use take the decat, for everyday legal driving, an ECE-approved HJS downpipe, for the middle road, a sports cat, knowing what that means at the technical inspection.

You will find all three types in the category Downpipe and GPF delete kits. If you are not sure which one fits your engine, write or call us. We will check fitment and availability before you order.

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