Shopping for an Audi S4 B9 exhaust is easy right up until you start reading. One thread says cat-back, another says downpipe, a third says the stock valved system is fine, and every listing promises more sound and more power. The truth: on the EA839 3.0T, the exhaust you choose depends on whether you want sound, power, or both, and on what else your build is running. We do not sell B9 exhaust parts, so this is a straight, unbiased guide to your options, plus the B9 supporting upgrades we do make, like 4 Bar MAP sensors for the EA839, that let a tuned exhaust build work properly.
Coming from a B8 or B8.5? That is a supercharged 3.0T and a different story; see our supercharged Audi S4 guide and Audi S4 mods roadmap.
How the Audi S4 B9 exhaust is laid out
The B9 and B9.5 S4 use the EA839 3.0T turbocharged V6, with the turbo sitting in the valley between the cylinder banks. That hot-V layout shapes everything about the exhaust:
- ✅ Turbo and catalyst: the turbo and the first catalyst live up top, near the back of the engine.
- ✅ Downpipes: carry exhaust down from the hot-V area to the underbody.
- ✅ Midpipe and resonators: run under the car. Some markets add a gasoline particulate filter (GPF, also called OPF) here.
- ✅ Rear section: mufflers, valves and quad tips. Many S4s use valves controlled through drive select.
Because the hottest, most restrictive hardware is packed near the firewall, a rear-only change mostly changes sound. Flow gains need work further upstream. For the vocabulary, see our turbo back exhaust explainer.
Audi S4 B9 exhaust options compared
Axle-backs and cat-backs are sound upgrades with few emissions questions. Downpipes and full systems are power upgrades that need a tune and touch emissions hardware. Resonator deletes are the cheapest way to get louder and the easiest way to get drone.
| Option | What it replaces | Main effect | Tune needed | Emissions questions |
|---|---|---|---|---|
| Axle-back / valved rear | Rear mufflers and tips | Sound | No | Few |
| Cat-back | Everything after the catalysts | Sound, some flow | Usually no | Few (check GPF cars) |
| Resonator delete | Center resonators | Louder, possible drone | No | Few |
| Downpipe | Hot-V downpipes, often catalysts | Flow and spool | Yes | Many |
| Full turbo-back | Turbo outlet to tips | Flow and sound | Yes | Most |
What to check before you buy
- ✅ Market and GPF: European-market cars from later years may have a particulate filter, which changes which systems fit. Confirm what your car has.
- ✅ Valves: make sure the system works with your factory valve control or includes a solution, or you may chase fault codes.
- ✅ Drone: deleting resonators on a daily driver can make highway cruising miserable.
- ✅ Engine: after the facelift, many European S4s switched to a TDI diesel. Make sure you are shopping for the EA839 petrol car.
- ✅ Legal: anything that removes catalysts is for off-road or competition use only.
Why supporting mods matter more than the pipes
Here is the part most exhaust pages skip. A freer-flowing exhaust on a tuned EA839 means more boost and more heat, and the factory hardware has limits. Chasing power with an exhaust while ignoring the rest is like buying bigger tires for a car with worn brakes.
4 Bar MAP sensors
The factory EA839 MAP sensors are 3 bar units, so they run out of range on higher-boost calibrations. Our Vorsprung 4 Bar MAP sensors are a direct upgrade for the 2.9T and 3.0T: two calibrated sensors per kit, plug-and-play with the factory harness, installed the same way as the originals. Prefer the dealer route? The OEM 4 bar part is 04E906051J.
Shop the B9 EA839 4 Bar MAP Sensors, $99.99
✅ Plug-and-play with the factory harness ✅ B9 fitment help from real EA839 owners ✅ Fast US shipping
Zeus EA839 ignition coils
More boost asks more of your spark. The Zeus Ignition Coil Upgrade Kit for the EA839 is a plug-and-play coil-on-plug set for the B9 and B9.5 S4, S5 and SQ5, rated for up to 10% more energy output than stock, without the Audi Tax. Misfires on a tuned car? Our Audi ignition coil replacement guide covers the symptoms.
Haken rear big brake kit
Going faster means stopping harder. The Haken Street Rear Big Brake Kit pairs a 4-piston caliper with a dedicated electronic parking brake caliper so you keep factory EPB function, and uses 356mm two-piece rotors. It is built to order with about a 45-day lead time, so confirm your exact chassis and parking brake type before ordering. More in our big brake kits collection.
TruShift transmission mount
The TruShift Transmission Upgrade Mount fits the B9 and B9.5 S4 and S5, using 65 durometer rubber to reduce drivetrain movement and sharpen shifts without harsh cabin vibration. At $19.99, it is the cheapest feel upgrade in this post. Read why in our transmission mount upgrade guide.
A sensible B9 S4 build order
- ✅ Want sound only: a quality valved cat-back or axle-back, and stop there.
- ✅ Want power: tune, then 4 Bar MAP sensors and coils as boost rises, then front-section exhaust work.
- ✅ Driving harder: add the transmission mount and brake upgrades as power climbs.
- ✅ Keep it road friendly: keep catalysts in place on any car that needs to pass inspection.
Off-road / competition use only: catless parts such as test pipes, catless downpipes and our HEH Headers remove or bypass factory emissions hardware. They are sold for off-road and competition vehicles and may not be legal on public roads where you live. Check your local laws before you buy.
Install notes
- ✅ Cat-backs are driveway jobs with jack stands and patience.
- ✅ Hot-V downpipes are much harder: tight access near the firewall and heat-seized hardware. Budget shop time.
- ✅ MAP sensors and coils are quick, plug-and-play swaps.
- ✅ Tune last, once the hardware is installed, so the calibration matches the car.
Audi S4 B9 Exhaust FAQ
What is the best Audi S4 B9 exhaust upgrade?
It depends on your goal. For sound, a valved cat-back is the easiest. For power on a tuned car, front-section work such as downpipes matters more, along with supporting parts like 4 Bar MAP sensors.
Does a cat-back add power on a B9 S4?
Usually only a little. The most restrictive hardware is near the turbo, so a cat-back mostly changes sound.
Do I need a tune for a B9 S4 downpipe?
Yes. Downpipes change airflow and catalyst hardware, and the car needs a calibration to run properly with them.
What is a GPF or OPF on the B9 S4?
It is a gasoline particulate filter fitted to some later European-market cars. It affects which exhaust systems fit, so confirm whether your car has one.
Why do I need 4 Bar MAP sensors on a B9?
The factory EA839 sensors are 3 bar units and cannot read higher boost accurately. Higher-boost calibrations need 4 bar sensors.
Does Vorsprung sell B9 S4 exhaust parts?
Not currently. We offer B9 supporting upgrades such as 4 Bar MAP sensors, Zeus EA839 coils, the Haken rear big brake kit and the TruShift transmission mount.
Will a resonator delete cause drone on a B9 S4?
It can. Resonators are there to cancel certain frequencies, and removing them often adds highway drone.
Are B9 S4 catless downpipes legal?
No. Catless parts are for off-road and competition use only and may not be legal on public roads where you live.
Bottom line on the Audi S4 B9 exhaust
Choose your Audi S4 B9 exhaust by goal: rear sections for sound, front sections plus a tune for power. Whatever you pick, back it up with the parts that keep a tuned EA839 happy, starting with 4 Bar MAP sensors, then coils, a transmission mount and brakes as the power grows.
Shop the B9 EA839 4 Bar MAP Sensors, $99.99
Prices checked September 25, 2026 and subject to change.
Drive the difference. Drive Vorsprung.
