Exhaust noise rules in QLD, minus the forum myths

Every week someone brings in an exhaust they bought online and asks why it got defected. Almost every time the answer is the same: nobody checked the actual rules before bolting it on. So here are the actual rules.

The number: 90 decibels, measured properly

For most passenger cars in Queensland the limit is 90dB under the stationary noise test — the meter sits half a metre from the exhaust outlet at a 45° angle, and the engine is held at a set RPM. That's not '90 decibels at any moment ever' — it's a specific test with a specific procedure.

The forum myth is that the test happens at idle or redline. It's neither — it's typically around three-quarter max governed RPM for the engine, which is where a badly designed system gets properly loud.

What gets you defected

• Removing or gutting the catalytic converter — that's an emissions defect and it voids insurance arguments too
• No muffler or a 'test pipe' resonator that does nothing
• Tips aimed up or sideways where the meter catches more noise
• Exhausts leaking before the muffler — yes, a crack counts

A yellow defect sticker means the car's off the road until it passes an inspection. The sticker costs more embarrassment than the exhaust cost money.

What the cops actually use

Roadside testing is usually a quick version of the stationary test. Some operations use drive-by measurement setups too. Either way, 'it came with the car' and 'it's only loud at full throttle' are not defences — if it fails the test, it fails.

How to be loud and legal

The trick nobody tells you: where the sound happens matters more than how much there is. Valved systems give you a quiet flap for the street and an open one for when it doesn't matter — they're the answer for anyone who wants noise sometimes. A properly designed performance exhaust with good resonators can sound genuinely angry while measuring legal, because the engineer tuned the frequency, not just the volume.

Every system that leaves our shop gets metered to the test standard before you take it. If your heart is set on something that won't pass, we'll tell you straight — and show you the valved version that gets you 90% of the way there without the sticker.