The 5 Best Engine Mods You Can Make To Your Audi B9 S5 (And S4, SQ5, etc.)

Audi’s B9 S4 and S5 are comfortable rocketships you can drive every day without a second thought. But next to some other European sport sedans, some may believe there’s room for improvement. The aftermarket certainly felt that way and has developed a substantial catalog for the B9 and the EA839 turbocharged 3.0T engine found in a bunch of other Audi products. As experts in the field, we know which of these you should prioritize, so here’s our top five Audi B9 performance and reliability upgrades.

034 Motorsport PCV Hose Upgrade

The 034Motorsport PCV Breather Hose is a direct-fit, high-durability replacement for the failure-prone OEM plastic hose in Audi’s EA839 V6 engines, offering reinforced silicone construction and billet aluminum check-valve components designed to withstand boost pressure and prevent crankcase overpressure. It maintains proper ventilation under both vacuum and boost conditions by safely isolating the crankcase from pressurized intake air, thereby reducing the risk of oil expulsion and potential engine fire—a known failure mode of the stock PCV system. Whether your vehicle is bone-stock or tuned through Stage 3, this upgrade provides reliable long-term performance and significantly enhanced safety across all power levels.

ECU & TCU Tuning

The APR UltraLink Tuning Cable is a plug-and-play, home-use tuning solution that lets you flash your vehicle’s ECU and TCU from the comfort of your home—no separate software required—via APR’s online UltraLink Marketplace, where you can buy, install, and update over 10,000 in-house developed tunes. It supports features like multi-stage tunes, octane selection, launch control, speed limiters, torque adjustments, exhaust sound modes, and more, while also allowing you to read/clear fault codes and reset flash counters. The UltraLink is fully unlocked for use on multiple vehicles, offers free updates for existing APR customers, and most tunes are even CARB-compliant.

Intake & Turbo Inlet Upgrades

The 034Motorsport X34 Carbon Fiber Intake System is a premium, OEM+ replacement for the stock airbox that enhances airflow, horsepower, and induction sound in B9/B9.5 Audi S4/S5 models with the 3.0 TFSI engine. Crafted with a sleek carbon fiber airbox and CFD-optimized intake tube, it features a massive unshrouded 5″ pleated cotton conical filter—ensuring significantly reduced intake air temperature and improved throttle response while maintaining a stealthy, factory-like appearance. The system delivers dyno-proven performance gains—approximately +19 hp and +20 lb-ft torque at ~4,950 RPM—while providing a straightforward, reversible installation with no permanent modifications required.

Intercooler & Charge Cooling Mods

The APR Intercooler System is a massive front-mounted, bar-and-plate air-to-air upgrade designed for 3.0 T B9/B9.5 Audi S4/S5 models; it boasts a significantly larger core—approximately 356.4 in² frontal area and 801.9 in³ volume—versus the factory unit’s 162.4 in² and 507.6 in³—resulting in substantially cooler intake charge and reduced heat soak for improved performance. Featuring smooth cast aluminum end tanks, layered silicone inlet/outlet hoses with EZ-Flow design, and TIG-welded construction, the kit is engineered to deliver high flow with minimal pressure drop and ensure reliable, leak-free operation. Plus, it’s a direct bolt-on upgrade with no trimming needed, offering a simple installation and dyno-proven gains—even when used with the stock ECU.

Downpipes & Exhaust Enhancements

This bolt-on exhaust modification is a direct-fit replacement for the front resonator on Audi B9/B9.5 S4, S5, and S5 Sportback 3.0T models, offering an easy install with no welding required. Constructed from 304 stainless steel, the kit delivers a deeper, more aggressive exhaust tone under acceleration—without adding cabin drone—and reduces weight compared to the stock resonator. It’s fully reversible and lets your Audi emit a sporty growl at a fraction of the cost of a full cat-back system- ask us how we know.

These components are just the start for what you can do to improve and bulletproof your EA839-equipped Audi B9 model. Many aftermarket companies offer the support you need to turn your S4 or S5 into the sport sedan of your dreams, and you can likely find their products here at FCP Euro. Before shopping, head to the Audi B9 Owners Hub to check out all FCP Euro offers for the fast Audi, from parts to content and expert knowledge. There, you'll have everything you need for your car in one easy web page.