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This BMW F30 runs a CMST valved cat-back exhaust: a dual twin-exit system in SUS304 stainless steel, with remote-controlled valves and carbon-fibre tips, fitted to a car converted to the M4 look. The system replaces the restrictive factory rear muffler with a freer-flowing, valve-equipped design that lets the driver switch between a quiet cruise and a loud, sharp note on demand. SUS304 stainless gives the corrosion resistance and light weight a performance exhaust needs, and the four carbon-tipped outlets finish the muscular rear bumper of the M4-style conversion.

• Vehicle: BMW 3 Series F30 (2012–2019), here with an M4-style rear bumper conversion
• Type: valved cat-back system, dual twin-exit (four outlets)
• Construction: SUS304 stainless steel with carbon-fibre exhaust tips
• Valves: vacuum-actuated, remote-controlled for on-demand sound
• Benefit: freer exhaust flow, switchable note, lighter weight, sharper rear styling

Why the exhaust matters on the F30

An exhaust system does more than make noise. How freely spent gases leave the engine affects how the whole car breathes and drives, and the factory rear silencer on the F30 is tuned for quietness and emissions compliance rather than flow or sound. A cat-back system — everything from the catalytic converter back — is the usual upgrade because it improves flow and transforms the note while leaving the emissions hardware in place. On this F30, the owner has gone a step further by pairing the CMST valved system with an M4-style rear bumper, so the quad outlets and aggressive diffuser look the part as well as sounding it.

SUS304 stainless construction

The system is built from SUS304 (304-grade) stainless steel, the material of choice for quality performance exhausts. SUS304 resists the corrosion that comes from heat cycling, condensation and road salt far better than mild or aluminised steel, so the system stays clean and structurally sound over years of use. It is also lighter than the cast and heavier-gauge factory rear section, trimming a little weight from the very back of the car. The mandrel-bent tubing keeps a consistent internal diameter through the bends, avoiding the flow-choking crush points of cheaper press-bent pipework.

How the valve system works

The defining feature is the valve. Each tailpipe path carries a butterfly valve, typically vacuum-actuated and operated through a remote control (and, on many setups, a switch or app). With the valves closed, exhaust gas is routed through a longer, more muffled path, keeping the car civil for early starts, built-up areas and long highway stints. Open the valves and the gas takes the shorter, freer route, releasing the system's full volume and a harder, sharper note. The result is one exhaust that behaves like two: quiet when you need it, loud when you want it. That on-demand control is why valved systems have become the default for street performance cars that still have to live with neighbours and noise rules.

Sound, flow and the carbon tips

With the valves open, the CMST system gives the F30's engine a noticeably more vocal, free-revving character — the kind of crisp, building note the source describes as raising the pulse of the driver and everyone nearby. Because the system frees up the rear of the exhaust, it reduces back-pressure compared with the restrictive factory muffler, which helps the engine breathe; on a forced-induction F30 this is felt as a more eager top end and a sharper throttle response rather than a headline power figure. We do not quote dyno numbers here because gains depend on the specific engine, tune and supporting modifications, and an exhaust alone is one part of that picture. What is consistent is the improvement in sound, flow and the quality of the experience.

The four carbon-fibre tips finish the system. Beyond their motorsport look, carbon tips stay cooler to the touch than polished steel and add a light, premium detail that suits the M4-style rear bumper. They are the visible signature of the system in the diffuser cut-outs.

Fitment in Australia

As a cat-back, the system bolts up to the factory mounting points behind the catalytic converters, so it is a direct-fit upgrade that does not disturb the emissions hardware. The valve actuation needs a vacuum or electronic feed and the control module wired in, so professional fitment is the sensible route — particularly to set the tip alignment cleanly in an M4-style rear bumper and to confirm the valves open and close correctly. A note on the law: exhaust noise is regulated in Australia and limits vary by state, so a valved system that can run quietly on the closed setting is a practical choice for keeping a loud car road-legal day to day. Have the install checked against your state's noise rules.

Explore the range in our CMST Catback Exhaust collection, see matching aero in our CMST Body Kit for BMW and BMW Body Kit ranges, and read about the brand on the CMST page.

FAQ

Does this exhaust fit my F30 3 Series?

The CMST valved cat-back is designed for the BMW F30 3 Series (2012–2019). Exact fitment depends on your engine and whether you run the factory or an M4-style rear bumper, so confirm your model and rear-bumper setup when ordering to get the correct tailpipe layout and tip spacing.

Will a cat-back exhaust pass an Australian noise test?

It can, because the valves let you run the system in its quiet (closed) mode. Australian exhaust-noise limits vary by state and are measured under defined conditions, so a valved system is a sensible choice for staying within the rules — but you should have the fitted car checked against your state's requirements rather than assuming compliance.

How much power will it add?

An exhaust alone typically delivers improved flow, throttle response and sound rather than a large headline power figure, and any gain depends on the engine, tune and other modifications. We do not quote dyno numbers because they would be misleading without the full specification; the reliable benefits are reduced back-pressure, a freer-revving feel and the switchable note.

Why SUS304 stainless steel?

SUS304 (304-grade) stainless resists corrosion from heat cycling, moisture and road salt far better than mild or aluminised steel, so the system lasts and stays clean. It is also lighter than the heavy factory rear section, and its mandrel-bent tubing keeps exhaust flow smooth through the bends.

Can I control the valves from inside the car?

Yes. The system uses remote-controlled valves, so you can open or close them on demand to switch between quiet and loud. Many installations also allow a dash switch or app control; the exact control method is set up during fitment.

Do the carbon tips get damaged by heat?

No. The carbon-fibre tips are designed for exhaust use and sit at the cooler outlet end of the system. They stay cooler to the touch than steel tips and hold their finish, which is why they are a popular premium detail.

Want a valved cat-back for your F30? Explore fitment, sound and finishes in our CMST Catback Exhaust range and talk to the AME Motorsport team about professional fitment in Australia.