Audi S4 / A4 B9.5 | Prepreg Dry Carbon Fiber Rear Diffuser

Audi S4/A4 B9.5 (2019-2023) Prepreg Dry Carbon Fiber Rear Diffuser

Engineered for Audi S4/A4 B9.5 (facelift, 2019-2023) sedan and Avant owners, this Prepreg Dry Carbon Fiber Rear Diffuser replaces the factory plastic part and delivers track-grade aggression to the rear of your sport sedan or wagon. Imported from leading manufacturers around the world and quality-controlled by BYC Performance, this Audi B9.5 carbon rear diffuser bolts directly to OEM mounting points: no cutting, drilling, or modification required.

If you're building a serious Audi S4 B9.5 tuning or A4 B9.5 modifying project and want a diffuser that exceeds the factory plastic in finish and performance, this dry carbon rear diffuser is built for you. Autoclave-cured prepreg carbon is noticeably lighter than wet-lay parts, with superior structural integrity and outstanding UV resistance. Matched to the sport-sedan character of the S4 B9.5's 3.0 TFSI V6 single-turbo (349 hp), this aggressive geometry is the ideal aesthetic and aerodynamic upgrade for street and weekend track use.

Key Features

• Prepreg Dry Carbon Technology: Pre-impregnated plies cured in an autoclave under high heat and pressure for a more consistent weave.
• Aggressive Rear Design: Sharp diffuser channels aligned with S4 sport-sedan DNA. Noticeably lighter than the factory plastic part.
• Race-Grade Strength: Carbon fiber offers very high strength for its weight.
• Aerodynamic Performance: Optimized channels accelerate underbody airflow and add downforce at speed.
• 2x2 Twill Carbon Weave: Authentic carbon pattern under a high-gloss UV-protective clear coat.
• Direct OEM Fit: Plug & play on factory Audi A4 / S4 B9.5 sedan and Avant rear-bumper mounting points.
• UV & Chemical Protection: Long-life clear coat resists fading, cracking, fuel splash, and road tar.

Prepreg Dry Carbon vs. Wet Carbon: Which Is Better?

Most aftermarket carbon parts are made using wet lay-up, with resin applied by hand and cured at room temperature. Prepreg dry carbon:

• Autoclave-cured under high heat and pressure → a more consistent weave
• A controlled resin ratio → lighter and stronger
• The production method widely chosen in motorsport
• Minimal UV fading over years of use

Installation Notes

Installing the Audi S4/A4 B9.5 carbon diffuser is a direct replacement of the factory part. Professional installation is recommended:

1. Raise the vehicle and remove rear bumper underbody screws.
2. Detach the OEM plastic diffuser from clips and bolts.
3. Test-fit the carbon diffuser for alignment.
4. Secure with supplied hardware to the manufacturer's recommended torque.
5. Verify exhaust tips are centered in diffuser cutouts (S4 quad-tip layout).

Care & Maintenance

Wash with pH-neutral car shampoo. Apply carbon-safe sealant every 6 months. Keep pressure washer nozzle at least 30 cm from surface.

FAQ

Does this fit B9 pre-facelift (2015-2019)?
No. This fits B9.5 (2019-2023) post-facelift cars. Pre-facelift B9 (2015-2018) owners should contact BYC for diffuser availability.

Does this fit the RS4 Avant?
No. The RS4 B9/B9.5 factory rear bumper has aggressive sport geometry; this diffuser is for A4 and S4 bumpers.

Compatible with A4 Avant (wagon)?
Yes. A4 Sedan and Avant B9.5 share the same rear-bumper mounting points; both body styles are fully compatible.

Compatible with previous-generation B8/B8.5 (2008-2015)?
No. B8/B8.5 is an entirely different platform.

Will rain damage dry carbon parts?
No. Autoclave-cured prepreg carbon is fully waterproof and weather-resistant.

Shipping time?
In-stock items ship within 1-3 business days via partner couriers. International shipping available. Parts sourced to order are delivered within 30 days of the order date at the latest.

Warranty?
Manufacturing defects are covered by a 24-month BYC warranty, in addition to your legal rights.

Why BYC Performance?

BYC Performance is a Turkey-based performance tuning specialist sourcing premium carbon fiber parts from leading manufacturers around the world and supplying them to the Turkish market. Our catalog includes Audi B9 carbon parts, Audi RS carbon diffusers, BMW M3 carbon diffusers, Porsche carbon spoilers, and many more high-quality carbon components. All parts are sourced from leading manufacturers around the world and undergo strict quality control.