Direct answer
An aftermarket exhaust is legal on an Australian light vehicle when the system still routes gas only where the manufacturer designed an outlet, keeps exhaust out of the occupant compartment, retains original catalytic converters, particulate filters and sensors in their original locations where those items were certified equipment, and meets the noise and emissions instruments your state applies on the day. VSB 14 holds the national technical text. Your registration authority holds the inspection method. This page does not print a decibel number.
Why the catalogue was a bad teacher
The old shop listed systems, mufflers, extractors, resonators and tips as separate categories. Inspectors do not. They look at the path from the manifold to the atmosphere and ask whether every certified control device is still in that path. A beautiful muffler behind a deleted catalyst is still a deleted catalyst.
Heritage exhaust URLs 301 to the performance hub or sit in this guide’s topic. Prices from those pages are not republished.
What a state guide actually says
Transport Victoria’s modification guide publishes a clear exhaust block that applies instead of one VSB 14 modification code for that jurisdiction. It requires that exhaust gases cannot enter the occupant compartment; that gases emit only from a place the manufacturer designed to emit them; that no part of the system passes through the passenger compartment; that catalytic converters remain in their original location with all gas flowing through them; that original sensors and particulate filters remain in their original locations and operational; and that ornamental or functional systems are not mounted so as to create a hazard. Read the live page for the full wording and any later amendment.
Other states may adopt VSB 14’s exhaust section more directly or publish their own information sheet. TMR Queensland, TfNSW and the remaining agencies on the state map are the places to confirm the method they use for noise — which can differ even when the hardware rule looks similar.
Catalysts, filters and sensors
If the vehicle was certified with a catalyst, oxygen sensors, a diesel particulate filter or a petrol particulate filter, those items are part of the type approval. Moving them, emptying them, or running a straight pipe around them is the modification most likely to fail both an inspection and an environmental complaint. “Decat for the track, cat for the street” is two vehicles. The street one has to match the register.
Sensors that move with a custom manifold can also drop you into a certified engine or exhaust code. Ask before you fabricate.
Noise without a made-up number
Jurisdictions publish or point at a noise test method. The method, the meter, and the site matter. A phone app is not that method. We will not invent a “legal dB” for a sports muffler because the figure, when it exists, is attached to a procedure and a vehicle class. If a seller quotes a number with no method, treat it as marketing.
Police and transport inspectors can still defect a vehicle that is unreasonably noisy under the in-service rules even if a workshop promised it would “pass”. Paperwork from a seller is not a state certificate.
Extractors, manifolds and turbo plumbing
Changing the manifold changes the engine’s breathing and often the position of sensors and catalysts. That is why extractor and turbo-manifold jobs sit closer to engine and powertrain than to a tip. If forced induction is added to a vehicle that was not certified with it, you are in certified territory. Heat shielding and routing still have to keep gas and heat out of the cabin and away from brake lines.
How to brief a workshop
Give them the state of registration, the date of manufacture, and a sentence that says “retain all certified emissions devices in their original locations; no cabin penetration; outlet only where the manufacturer designed one.” Ask them to write the part numbers and the VSB 14 section they believe applies on the invoice. If they cannot name a section, find a shop that can — or take the question to a signatory first.
Related pages
Check with your state regulator or engineer before you change an exhaust path. This guide is general information, not a noise certificate.
A brief you can paste to a fabricator
“State of registration: [state]. Date of manufacture: [date]. Retain every catalytic converter, particulate filter and exhaust sensor the vehicle was certified with, in its original location, with all gas flowing through those devices. No exhaust in or through the occupant compartment. Outlet only at a manufacturer-designed emission point. No ornamental system that creates a hazard. Cite the VSB 14 exhaust section and the state information sheet you are working to on the invoice.”
If a fabricator strikes out the catalyst line, you do not have a street exhaust. You have a different vehicle.
Heat, mounts and the parts that are not the muffler
Hangers, shields and clearance to brake hoses and fuel lines are part of the system. A legal path that sags onto a hose is not a finished job. Heat in the cabin is a failure of the “no gas and no hazard” idea even when a meter would still pass a noise test. Walk the path with a light before you paint the tip.
Track use and the two-vehicle problem
A weekend car that runs an open pipe on a circuit and a compliant system on the road is two configurations. Only the compliant one belongs on the register. Swapping in a car park on the way home is how people collect defect notices. If you truly have two systems, the street one has to be complete — converters, sensors, mounts — not a souvenir muffler hanging off a race dump.
Related
Performance, engine and powertrain, state rules. Check with your state regulator or engineer before you change an exhaust path.
Sensors that move when the manifold moves
Oxygen sensors, temperature sensors and, on some diesels, pressure sensors are part of the certified path. A custom manifold that “has a bung” is not the same as a sensor in its original location and original operational context. Victoria’s published exhaust block is explicit about original locations. Other agencies point at VSB 14’s exhaust section. Either way, moving a sensor is a fact you put in the first email, not a surprise on inspection day.
Cabin integrity
Flexible couplings, rusted floor pans and poorly sealed gearboxes are how people discover that “no gas in the cabin” is a living requirement. After a system goes on, sit in the car with the engine loaded and the windows shut. If you can smell exhaust, you do not have a finished street system. That test is not a substitute for a state noise method. It is a test for the requirement every guide agrees on.
Check with your state regulator or engineer before you change an exhaust path.
New and used systems
A second-hand exhaust can be lawful if it still contains the devices the vehicle was certified with and still meets the routing rules. It can also be a pipe that someone else already emptied. Look through it. Ask. If you cannot see a converter where the certified vehicle had one, do not fit the system on a street car.
New systems have the opposite problem: marketing. “Cat-back” should mean the converter stays. If the listing photographs a straight path where the converter was, believe the photograph.
Motorbikes and light commercials
This guide is for light motor vehicles in the VSB 14 sense. Motorcycles and some light commercials have extra or different noise instruments. Do not apply a passenger-car muffler argument to a bike and assume the same method. Ask the agency that issued those plates.
Complaints, neighbours and the police pathway
Noise complaints are how some exhausts meet an inspector without a booked roadworthy. The method they use is still the state’s method, not a phone app and not a seller’s promise. If you are building a street car that will live in a dense suburb, design to the sheet, not to a clip.
Related: performance, engine and powertrain. Check with your state regulator or engineer before you change an exhaust path. This guide is not a noise certificate and not a workshop instruction.
Closing checklist
Before you present the car: confirm converters and filters are present and in path; confirm no cabin smell under load; confirm the outlet is a manufacturer-designed point; confirm hangers and shields are sound; confirm the invoice names the section. Then use the state method if an inspector asks for noise, not a phone app.
Check with your state regulator or engineer before you change an exhaust path.
Why this page refuses a decibel headline
A decibel headline without a method is how the old web misled modifiers. The number that matters is attached to a state procedure, a meter and a site. Until you have those three, you do not have a number worth writing down. Design to the hardware rules — path, catalysts, cabin integrity — and let the state method do the rest on the day.
Check with your state regulator or engineer before you change an exhaust path.