Audi R8 V10 exhaust silencer 420.251.051

Part Number: 420.251.051 (Base part number)

Common Revisions: * 420.251.051.TX (Facelift V10/V10 Plus)

• 420.251.051.RX (Pre-facelift replacement unit)

• 420.251.051.GX (Specific V8/V10 Spyder crossover applications)

  Generation: Type 42 (Gen 1 & Gen 1.5 Facelift)

  Engine: 5.2L FSI V10

The 420.251.051 series refers to the heavy-duty rear exhaust silencer assembly for the first-generation Audi R8. Because the R8 is mid-engined, the silencer sits directly behind the engine and just forward of the rear bumper, making it a critical component for both thermal management and the signature V10 acoustic profile.

Technical Specifications

• Construction: Stainless Steel (AISI 304L) with high-density acoustic packing.

• Weight: Approximately $24\text{ kg} – 28\text{ kg}$ (OEM units are notably heavy compared to titanium aftermarket options).

• Valving System: Features dual vacuum-actuated valves (flaps).

  • Closed: Exhaust gases are routed through a series of internal baffles to meet noise regulations and prevent cabin drone.

  • Open: (S-mode/Sport) Gases bypass several chambers for a “straight-through” effect, increasing the decibel level and reducing backpressure.

• Fitment: Connects to the primary catalytic converters via specialized spring-loaded clamps (420.251.143).

Revision and Suffix Breakdown

When sourcing this part, the suffix after “051” is vital for compatibility:

• “TX”: Found on 2014–2015 Facelift models. These are often optimized for the 7-speed S-tronic gearbox shift-blip acoustics.

• “RX”: Typically a factory remanufactured or replacement code for the 2009–2012 Pre-facelift V10 models.

• “GX”: Often associated with the 4.2L V8 or early Spyder models. While the external dimensions are similar, the internal baffle design differs to match the V8’s pulse frequency.

Professional Installation & Maintenance

1. Heat Soak: Because the silencer is encased in a tight space behind the V10, the heat shields (Part No. 420.825.671) must be in perfect condition. Damaged shields can lead to the melting of the rear bumper or damage to the parking sensor wiring harness.

2. Vacuum Line Check: If your R8 sounds “quiet” even in Sport mode, or if it sounds permanently “loud,” the vacuum lines leading to the actuators on the silencer have likely perished or slipped off. These lines are exposed to extreme heat and are a common failure point.

3. Spring/Clamp Replacement: The silencer is mounted using a heavy-duty spring kit (893.253.353). Never reuse these springs if they show signs of rust or heat fatigue, as a loose silencer will cause significant vibration through the chassis.

4. Tailpipe Alignment: The silencer does not actually touch the oval or round exhaust tips seen in the bumper; those are “floating” finishers. Proper alignment of the silencer ensures the exhaust gases exit centrally through those finishers without scorching the trim.