GR Supra Downpipe: Catted vs Catless – Is Catless Legal in Australia?

Catted vs catless downpipes for the GR Supra B58: power, sound, check engine lights, and whether catless is legal on Australian roads. Includes AUD prices.

5 min read

If you've decided to take your GR Supra to Stage 2, the downpipe is the part you can't skip. The first question everyone asks is: catted or catless? The second, for Australian owners, is: is a catless downpipe legal here? This guide answers both and compares the downpipes we stock, with AUD prices.

What does a downpipe do on the B58?

The downpipe bolts to the turbo outlet and carries exhaust gas into the rest of the exhaust. On the A90/A91 Supra, the factory downpipe has a dense catalytic converter built in, which is one of the biggest restrictions in the system. HKS, for example, compares its 150-cell sports cat with the stock 600-cell unit. A high-flow 4.5" downpipe reduces back pressure, so the turbo:

  • spools faster, with sharper throttle response
  • makes more power, especially with a Stage 2 tune
  • sounds deeper, with more turbo whistle

Catted downpipes: pros and cons

A catted downpipe replaces the factory cat with a high-flow catalytic converter, usually 100 to 400 cells per square inch (CPSI).

Pros: it keeps a working catalytic converter, it's much less likely to trigger a check engine light (many run with no CEL on a proper tune), it smells less, it drones less and it suits a daily driver.
Cons: it costs more, and it flows slightly less than a catless pipe at the very top end.

Catless downpipes: pros and cons

A catless downpipe is a straight pipe with no catalytic converter.

Pros: maximum flow, the lowest price and the most aggressive sound.
Cons: it needs a tune to avoid fault codes, it smells of raw exhaust, it drones more, and most importantly it is not legal on a registered road car in Australia.

Is a catless downpipe legal in Australia?

For a registered road car, no. Every Australian state and territory prohibits removing or tampering with a vehicle's emissions control equipment, including the catalytic converter. Vehicles also have to keep meeting the emissions and noise standards they were built to. Driving a road car without its cat can lead to fines, a defect notice or a failed roadworthy, and it may affect your insurance.

That's why we sell catless downpipes for off-road, competition and track use only. If your Supra is road-registered and driven on the street, fit a high-flow catted downpipe. You still get most of the Stage 2 gains and none of the legal risk.

This is general information, not legal advice. Rules and enforcement differ between states, so check with your state's road and environment authorities for your own situation.

Best catted downpipes for the GR Supra (AUD)

Catless downpipes (off-road and competition use only)

See the full range in our GR Supra downpipes collection.

Which GR Supra downpipe should you choose?

Choose based on how you use the car:

  • Daily driver on a budget: the VRSF 200-cell catted downpipe. It has a real catalytic converter, strong flow and the lowest price for a catted pipe.
  • Daily driver who wants the best quality and no CEL: the Active Autowerke Signature GESI or AMS Street. The GESI cats are known for staying free of check engine lights, and both are built to handle serious power.
  • Refined, emissions-tested JDM option: the HKS Metal Catalyzer. It's WLTC emissions tested and made for owners who want more flow without a loud car.
  • Dedicated track or competition car: a catless pipe such as the Sequential Racing 4.5" or Active Autowerke catless, as long as the car isn't driven on public roads.

Cell count explained: 100, 150, 200 or 400 CPSI?

CPSI (cells per square inch) describes how dense the catalytic converter's core is. A lower cell count flows more but cleans the exhaust less. A higher cell count is cleaner and less likely to set a check engine light, but flows slightly less. The factory Supra cat is about 600 cells. That's why dropping to 150–400 CPSI makes such a big difference while still keeping a working cat. Metallic substrates (as used in GESI cats) also handle heat and high power better than cheap ceramic cores.

Will a downpipe make my Supra drone?

Most of the drone in a modified Supra comes from the cat-back rather than the downpipe. A catted downpipe on a factory or quality aftermarket cat-back is usually fine on the freeway. Catless pipes, especially with a straight-through cat-back, are where drone and rasp become noticeable. If you want to control the noise, a valved exhaust such as the Valvetronic Designs system lets you close the valves when you're cruising.

Do I need a tune with a downpipe?

Yes. A downpipe changes how the exhaust flows, and the ECU needs a matching map to get the most from it and to avoid fault codes. That means unlocking the ECU first: a bench unlock for pre-06/2020 cars, or the FEMTO unlock for 06/2020+ cars. After that, a Stage 2 map is loaded. For the complete build path, read our GR Supra Stage 1 and Stage 2 mods guide.

Keep your factory downpipe

Whatever you fit, keep the original downpipe. If you sell the car, need to return it to stock for an inspection, or move to a different setup, having the factory part makes life much easier. It also helps resale, because many buyers want the option of returning the car to standard.

Installation

A B58 downpipe swap means working around the subframe and oxygen sensors, so it's best done on a hoist. We fit downpipes at our Melbourne workshop. See downpipe installation in Melbourne.

Frequently asked questions

How much power does a downpipe add to a GR Supra?

On its own, not much. Paired with a Stage 2 tune, the downpipe is what lets the B58 make its biggest bolt-on gains. Actual numbers depend on the tune, fuel and supporting mods.

Will a catted downpipe throw a check engine light?

High-flow catted downpipes such as the Active Autowerke GESI are designed to run without a CEL. You should still run a matching tune.

Which is louder, catted or catless?

Catless is louder and raspier. A quality catted downpipe adds a deeper tone and more turbo noise without the drone.

Can I fit a downpipe without changing my exhaust?

Yes. The downpipes we stock connect to the factory cat-back, and to most aftermarket cat-backs.

Is a catless downpipe legal in Australia?

Not on a registered road car. Catless downpipes are sold for off-road and competition use only.

With the release of the GR Supra in 2020, we witnessed the culmination of a two-decade-long anticipation. The GR Supra also referred to as the MK5, underwent a remarkable transformation, blending its iconic JDM heritage with contemporary design elements, including contributions from the renowned BMW Z4 platform. While some may perceive this collaboration as a departure from tradition, it's undeniably a testament to the enduring allure of the Supra lineage, echoing the legendary 2JZ engine resonating through to the B58.

Behind the wheel of the GR Supra becomes the focal point of admiration, drawing fellow enthusiasts and eliciting spontaneous snapshots from passing people. My own journey into automotive culture was shaped by the vibrant scene of the 90s, particularly growing up in Melbourne, where car salons and cultural exhibitions brought JDM customization to life, from slammed suspensions, to under glow lights, supercharged turbos adorning from the streets to showroom exhibition floors.

Amidst the rapid evolution of the Australian automotive landscape, I recognized an opportunity to cultivate the car community around the modification and enhancement of the GR Supra. This endeavor is dedicated to providing a specialized platform centralised enabling high quality products sourced into Australia for car enthusiasts like myself on the limitations of the GR Supra (Unlike US and Japan).

While the Australian market for car modifications may be comparatively modest in scale compared to regions like Asia, USA, or Japan, our aspiration is to create this community from an inclusive space where like-minded individuals can access products, meet, share insights from a the collective experience of automotive enthusiasts across the nation- and hopefully one day globally.

Join Sequential Racing Australia as we embark on this journey, celebrating the legacy of the supra and championing the spirit within Australia's dynamic car modification community forging connections through our shared passion for automotive culture.

Thank You
From All of Sequential Racing Team

Written By:  Phil L | 989.Supra (Director & Founder)