A downpipe is the single biggest restriction between your turbo and the atmosphere. Replacing it is usually the first hardware step on a modern forced-induction car — but the choice between a catted and a catless pipe changes how the car drives, sounds and passes inspection. Here is how we specify them.
What a downpipe actually changes
The factory downpipe carries the exhaust from the turbine housing into the mid-pipe, and on almost every OEM car it also holds the primary catalytic converter. That catalyst is a deliberate restriction: it is sized for emissions durability over 200,000 km, not for flow.
Reducing backpressure after the turbine lets the turbo spool sooner and hold boost with less effort. That is why a downpipe pairs so well with a calibration — the ECU can finally use the airflow the hardware allows. Browse what we make in performance downpipes.
Catted downpipes
A catted pipe keeps a catalyst, but a high-flow one: a larger substrate with a lower cell density than the OEM brick. You give up a small amount of peak flow and get back emissions compliance and a quieter, cleaner-smelling car.
- Keeps the car road-legal where emissions equipment is inspected
- No sulphur smell, far less rasp in the cabin
- Typically within a few horsepower of a catless pipe on a street tune
Catless downpipes
A catless pipe removes the catalyst entirely. It is the maximum-flow option and the right answer for a track car, but it has consequences you should decide on deliberately rather than discover later.
On a stock calibration a catless downpipe is worth almost nothing. The gains people quote come from the tune that accompanies it.
What to expect on the road
Expect a louder, harder-edged tone under load, a noticeable smell on cold start, and a check-engine light unless the ECU is adjusted for the missing catalyst. None of those are faults — they are what the part is.
Side by side
| Consideration | Catted | Catless |
|---|---|---|
| Peak flow | Very good | Best |
| Emissions equipment retained | Yes | No |
| Check-engine light risk | Low | High without a tune |
| Cabin noise | Moderate | Loud |
| Best suited to | Daily driven | Track / off-road use |
How we would spec it
If the car sees public roads and you want to forget about it: catted, with a Stage 2 calibration sized for it. If the car is a dedicated track weapon and noise and emissions are not constraints: catless, tuned.
Either way the fitment has to be exact. Tell us your chassis code and we will confirm the right part — start with our exhaust systems or reach out directly.
