Milltek Secondary Catalyst Bypass for BMW 3 Series G80 M3 & M3 Competition S58 3.0 Turbo (North American/ROW Non-OPF/GPF Cars Only) (2021 onwards) – Maximum Flow, Motorsport Use
This is Milltek's large-bore downpipe and de-cat for the BMW 4 Series G82 M4 & M4 Competition S58 3.0 Turbo (North American/ROW Non-OPF/GPF Cars Only). It replaces the factory downpipe with a larger-bore pipe and removes the catalytic converter entirely, clearing the single most restrictive point in the exhaust for the biggest flow gain available at this position in the system. It's usually fitted alongside a Stage 2 remap, since the ECU needs to be told to expect the different readings the lambda sensors give once the cat's gone. It's offered in non-resonated or resonated versions, so you can pick the setup that suits how the car's used.
It's built for owners already committed to a serious power upgrade rather than a casual bolt-on, so pair it with the matching Milltek cat-back system for the full effect.
Because it removes the cat, it's intended for off-road and competition use. A de-catted car will fail an MOT emissions test and isn't legal to use on UK roads.
Specifications
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System Type: Secondary Catalyst Bypass
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EC Approved: No
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Race System: Yes
Key Features
- Made from T304L aircraft-grade stainless steel, which is anti-magnetic and resists discolouration
- Mandrel-bent pipework keeps a constant diameter through every bend for unrestricted flow
- Removes the factory catalyst for maximum flow (off-road and competition use only)
- Resonated (quieter) or non-resonated (louder) versions
- Designed, developed and manufactured in the UK by Milltek Sport
Fitment
- BMW 3 Series G80 M3 & M3 Competition S58 3.0 Turbo (North American/ROW Non-OPF/GPF Cars Only) (2021 onwards)
- BMW 4 Series G82 M4 & M4 Competition S58 3.0 Turbo (North American/ROW Non-OPF/GPF Cars Only) (2021 onwards)
Not suitable for: the BMW 3 Series F80 M3 & M3 Competition Saloon (Non OPF/GPF Models Only), which needs the Milltek Downpipe & De-cat BMW 3 Series F80 M3 & M3 Comp Saloon Non OPF/GPF 14-18; the BMW 3 Series F30 328i M Sport Automatic (without Tow Bar, Non-xDrive & N20 Engine Only), which needs the Milltek Downpipe & De-cat BMW 3 Series F30 328i M Sport Automatic (without Tow Bar, Non-xDrive & N20 Engine Only) 12-15; the BMW 3 Series E30 M3, which needs the Milltek Full Exhaust & Cat Bypass BMW 3 Series E30 M3 87-92.
Installation
The fitting time varies by version; see the specification table for the option you choose. Some versions: Secondary Cat Bypass - Non Resonated - Fits to OE Downpipes & Axle Back System Only - Requires OE system to be cut. Some versions: Secondary Cat Bypass - Non Resonated - Fits to OE Downpipes & Milltek Sport Axle Back System Only. Some versions: Secondary Cat Bypass - Resonated - Fits to OE Downpipes & Axle Back System Only - Requires OE system to be cut. Some versions: Secondary Cat Bypass - Resonated - Fits to OE Downpipes & Milltek Sport Axle Back System Only. This work involves removing parts close to the turbo and engine, so we recommend fitting by a specialist with a ramp and suitable software support.
Upgrade Further
Also available from Milltek for this car: Milltek Filter-back Exhaust BMW 3 Series G80 G81 M3 Comp S58 3.0 Turbo OPF/GPF Touring XDrive 20+.
What's the difference between the resonated and non-resonated versions?
The resonated version adds extra silencing for a quieter, more refined tone. The non-resonated version leaves it out, so it is louder and more aggressive.
Will it fit the BMW 4 Series G82 M4 & M4 Competition S58 3.0 Turbo (North American/ROW Non-OPF/GPF Cars Only)?
Yes. Milltek lists this part for the BMW 4 Series G82 M4 & M4 Competition S58 3.0 Turbo (North American/ROW Non-OPF/GPF Cars Only) as well as the other models in the fitment list above.
Does it fit the BMW 3 Series F80 M3 & M3 Competition Saloon (Non OPF/GPF Models Only)?
No. For that car, choose the Milltek Downpipe & De-cat BMW 3 Series F80 M3 & M3 Comp Saloon Non OPF/GPF 14-18.
Is it road legal?
No. Removing the catalyst means the car will fail an MOT emissions test, so it is for off-road and competition use only.
Do I need a remap?
A suitable remap is strongly recommended, as the engine management needs to account for the change in flow and sensor readings. Speak to your tuner before fitting.
Can I use it with my standard exhaust?
Yes. Milltek lists it for use with the factory (OE) exhaust system.
Will removing the cat cause a warning light?
Without suitable software it is likely to, as the ECU expects the readings a working catalyst gives. This is why Milltek pairs it with a remap.
How long does it take to fit?
It depends on the version. Milltek's fitting time for each option is shown in its specification table.
What is it made from?
T304L aircraft-grade stainless steel, which is anti-magnetic and resists discolouration better than lower grades.
