A downpipe is one of the most popular upgrades for any turbocharged car, and one of the most misunderstood. Here's the plain-English version, from a qualified mechanic, of what it does, what the law says in Australia and how to choose.
What a downpipe does
The downpipe is the section of exhaust bolted directly to the turbocharger outlet. On most modern turbo cars the factory downpipe carries the main catalytic converter, and it's one of the biggest restrictions after the turbo itself. A larger, smoother aftermarket downpipe lowers backpressure, which lets the turbo spool faster. With the right tune, it can unlock meaningful power and torque gains.
Catted vs catless: the difference
- Catted (high-flow catted) downpipes keep a catalytic converter in the system, usually a high-flow unit with fewer cells than factory. You get most of the flow benefit while still treating exhaust emissions.
- Catless downpipes remove the catalytic converter completely. They flow the most, but they sound harsher, smell stronger and will almost always trigger a check engine light without a tune.
The legal side in Australia
Every Australian state and territory has rules against removing or tampering with a registered vehicle's emissions control equipment, and the catalytic converter is part of that equipment. That means a catless downpipe is not road-legal on a registered road car. It can also land you with a defect notice or a failed roadworthy, and it may affect your insurance. Catless parts are sold for off-road and competition use only.
A catted downpipe is the sensible choice for a car that's driven on the road. Exhaust modifications still need to meet noise limits and your state's modification rules, though, so check your state's requirements (or speak to a licensed vehicle engineer) before fitting. This is general information, not legal advice.
Do I need a tune?
For a catless downpipe, yes: without one you'll get a check engine light and you won't see the full gains. For a high-flow catted downpipe, a tune is still strongly recommended. It's how you actually get the power, and it keeps the engine's fuelling and boost where they should be.
Install tips from the workshop
- Always use new gaskets and hardware. Reusing old studs and nuts on a hot exhaust is asking for leaks.
- Soak the factory fasteners with penetrant the night before; turbo studs can seize.
- Take care with the oxygen sensors when removing and refitting them, and use anti-seize on the threads.
- Re-check torque after the first few heat cycles.
Downpipes we carry
- B58 downpipe: Supra 3.0 and BMW M340i, M440i, M240i and more (catted or catless)
- B46/B48 downpipe: Supra 2.0 and BMW 330i, 230i and more (catted or catless)
- Civic Type R FK8 and FL5 downpipe (catted or catless)
- VW Golf MK7 GTI downpipe (catted or catless)
- Audi S4/S5 B9 downpipe (catted or catless)
Not sure a part suits your car? Email andrew@clippingpointco.com with your year, model and engine before ordering. As a qualified mechanic, I'll check fitment for you.