Audi S4 Catalytic Converter B7 (2004–2008)

The catalytic converter for the Audi S4 B7 (2003-2008, 4.2 V8 Quattro, 344 HP) is a vital component of the exhaust system that reduces harmful emissions. It is designed to filter exhaust gases to meet emission standards while maintaining engine performance. It is available in original equipment manufacturer (OEM) versions and high-flow stainless steel sport replacements.

OEM catalytic converters for Audi S4 B7 typically come with ventilated non-perforated brake discs and have these diameters:

• Rear axle side (A4 B7 Avant S4 4.2 Quattro): 300 mm diameter
• Front axle side (A4 B7 S4 4.2 Quattro): 312 mm diameter

Sport stainless steel high-flow Milltek replacements fit B6/B7 4.2 V8 models, featuring tube diameters of 57.15 mm to 63.5 mm, TIG welded connections, and specific flanges for precise fitment.

Sport high-flow catalytic converters, such as those from Milltek, offer several advantages over OEM parts:

• Reduced exhaust flow restriction
• Improved horsepower and torque gains (estimated +5-15 HP)
• Made from durable stainless steel with TIG welding
• Designed for precise fit with specific flanges
• Compatible with factory or specially designed cat-back exhaust systems

Note: These converters maintain compliance with many emission standards but removing or modifying catalytic converters for street use may be illegal in some regions.

Aftermarket exhaust lines designed to replace or follow the catalytic converter include:

• Milltek and Diapason Motorsport cat-back systems with 57.15 mm diameter piping and aggressive quad or twin 76.2 mm exhaust tips
• 034Motorsport high-flow stainless steel systems with TIG welding and precision flanges (mainly for 2.0T/FSI but illustrates high-quality build)

These systems focus on enhancing exhaust sound, reducing backpressure, and improving overall performance.

Genuine brand-new, high-performance catalytic converters made in Europe to manufacturer specifications are available from trusted factory direct suppliers. They ensure compliance with emission regulations and come with warranties. These parts are made of stainless steel INOX 409 and equipped with advanced monolith substrates for durability and performance.

• Ensure compatibility by checking the engine displacement, vehicle model, and VIN
• Ask for installation manuals or technical support when purchasing
• Look for suppliers offering free returns within 30 days on unused parts and at least 3 years warranty

Removing or gutting the catalytic converter (known as decatting) can increase exhaust sound and flow but is illegal on public roads in many countries. High-flow sport catalytic converters offer a legal alternative by reducing restrictions while still filtering emissions.

It is important to maintain proper sensors (e.g., oxygen/lambda sensors) and comply with Federal EPA or European emission regulations to avoid check-engine lights or legal issues.

• Sport high-flow catalytic converters maintain a more civilized exhaust smell compared to no-cat setups
• Replacements should be matched with compatible exhaust components for best results

Correct fitment is ensured by selecting the catalytic converter model compatible with your specific Audi S4 B7 year, engine type, and transmission. OEM dimensions and aftermarket part specifications should be verified before purchase.

• Verify sensor locations and connection flanges
• Replace oxygen sensors when installing a new catalytic converter
• Professional installation by a specialized garage is recommended

Improper installation can cause malfunctions, shortening product life and voiding warranties.

High-quality new catalytic converters often come with a 3-year warranty or coverage up to 100,000 km, ensuring durability and performance under proper use. Warranty covers defects if installation instructions are followed, including use of original gaskets and sensors and professional fitting.

Many suppliers offer:

• Free return policies within 30 days for unused, original condition products
• Technical support via email or phone for installation guidance
• Analysis services for used converters to diagnose failures
• Loyalty programs or buy-back services for used parts to reduce waste

Always keep your purchase invoice and installation details for warranty claims.