Audi RS4 RS5 B9 Downpipe Catless High Flow 2.9 TFSI

The TOWMA High-Performance Downpipe for the Audi RS4/RS5 B9 unleashes the full potential of the 2.9 TFSI bi-turbo V6 engine. This upgrade delivers maximum flow, a raw RS sound, and forms the perfect foundation for a serious performance setup. Available as a catless or with a high-flow sports catalytic converter.

Advantages

• Maximum flow — free diameter for minimum restriction
• More power — 25-35 extra hp with ECU tuning
• Faster turbo response — less backpressure, faster spooling
• Raw RS sound — deep, powerful V6 bi-turbo note
• OEM+ fit — direct mounting without modifications
• T304 Stainless Steel — High-performance stainless steel for extreme temperatures
• TIG welded — perfect welds for optimal strength and flow
• Optional heat shield — extra thermal protection

Material & Construction

The TOWMA downpipe is manufactured from high-quality T304 stainless steel and fully TIG-welded for optimum strength and flow.

The free diameter pipe without internal restrictions ensures maximum exhaust flow, resulting in:

• Faster turbo response — both turbos spool up faster
• More power — especially in the mid-range rev range
• Better throttle response — more direct throttle response
• Higher top speed — less exhaust restriction

Available in two variants:

1. Catless (without catalytic converter):

• Maximum flow and performance
• Loudest, most aggressive RS sound
• Maximum power gain (30-35 hp with tuning)
• Not MOT-proof in the Netherlands
• For track/export use only

2. High-Flow Sports Catalyst (200-cell):

• Balance between performance and emissions
• Sporty RS sound, slightly less loud than catless
• Good power gain (25-30 hp with tune)
• Possibly MOT-proof (depending on inspection)
• Suitable for daily use

Optional heat shield:

For additional thermal protection, the downpipe is optionally available with a heat shield. This protects surrounding components from the extreme heat of the turbochargers.

Performance & Sound

Capital gain:

• Catless: +30-35 hp with ECU tuning (Stage 2)
• High-flow cat: +25-30 hp with ECU tuning (Stage 2)
• Without tuning: +10-15 hp (only due to better flow)
• Total power with Stage 2: 500+ hp possible!

Sound character:

The TOWMA downpipe transforms the 2.9 TFSI bi-turbo V6:

• Idle: Deeper, more present V6 bass
• Acceleration: Aggressive turbo whoosh and wastegate flutter
• High revs: Loud, race-inspired RS sound
• Deceleration: Pops and bangs (with tune)
• Downshifts: Aggressive backfire and crackling

Note: Catless is very loud. High-flow cat is sportier but more bearable for everyday use.

Installation & Assembly

The downpipe is designed for plug-and-play installation on the original Audi mounting points.

Installation steps:

1. Lift the RS4/RS5 and place it on a lifting platform
2. Remove original downpipe (3 bolts top, 2 bolts bottom)
3. Install new TOWMA downpipe with supplied gaskets
4. Install optional heat shield (if ordered)
5. Tighten all bolts to specifications (45-50 Nm)
6. Check for leaks upon initial start-up
7. Reset error codes (if present)

Installation time: 2-3 hours for an experienced Audi specialist

Recommendation: Professional installation by a certified Audi specialist or tuner is recommended.

ECU Tuning: For optimal performance, Stage 2 ECU tuning is HIGHLY recommended. The downpipe alone provides 10-15 hp, but with Stage 2 tuning, it adds 25-35 hp. Popular tuners: APR, Unitronic, IE, GIAC.

Compatibility

Suitable for:

• Audi RS4 Avant B9 (2018+) — 2.9 TFSI bi-turbo V6
• Audi RS5 Coupé B9 (2018+) — 2.9 TFSI bi-turbo V6
• Audi RS5 Sportback B9 (2018+) — 2.9 TFSI bi-turbo V6

Not suitable for:

• Audi RS4 B8 (2012-2015) — other engine (4.2L V8)
• Audi RS5 B8 (2010-2015) — other engine (4.2L V8)
• Audi S4/S5 B9 — other engine (3.0 TFSI V6)

Note: This is only for the B9 generation (2018+) with the 2.9 TFSI engine. Check your engine code before ordering.

Technical Specifications

Maintenance & Warranty

Maintenance:

• Check flanges for leaks regularly
• Inspect gaskets annually
• Check heat shield for damage (if fitted)
• Clean the outside with stainless steel cleaner for a shine
• Check mounting bolts for tightness

Warranty:

TOWMA offers a 3-year warranty on construction, fit, and finish. The warranty covers manufacturing defects, leaks, and fit issues. Damage due to improper installation, accidents, or misuse is not covered by the warranty.

Note: Installing a downpipe may affect your manufacturer's warranty. Check with your dealer before installing.

Frequently Asked Questions

• Do I need ECU tuning? Not required, but highly recommended. Without tuning, you'll gain 10-15 hp, and with Stage 2 tuning, you'll gain 25-35 hp.
• Is this MOT-proof? Catless is NOT. High-flow cat is possible, depending on inspection.
• How loud is this? Catless is very loud. High-flow cat is sporty but more bearable for everyday use.
• Will I get a check engine light? Possibly. This can be resolved with Stage 2 tuning or O2 sensor spacers.
• What is Stage 2 tuning? Stage 2 is ECU tuning specifically for downpipe upgrades. Stage 1 is software only, Stage 2 is software + hardware (downpipe).
• Do I need the heat shield? Recommended for extra protection, but not mandatory.
• Will this fit my RS5 Sportback? Yes, all B9 RS4/RS5 variants share the same engine and exhaust layout.