Ultimate B9 RS4 Upgrade Guide
The wagon you keep — a complete pathway from OEM+ to Stage 2 on the 2.9 TFSI V6.
Audi RS4 B9The B9 RS4 is the platform Audi quietly perfected. The 2.9 TT V6 has substantial headroom — but it rewards a structured build, not a parts dump.
Software and downpipes
Mature Stage 1 hardware pathways respond cleanly on the OEM downpipes. Once you commit to high-flow downpipes the Stage 2 hardware pathway — completed before any external calibration — becomes the foundation of everything that follows.
Cooling
The OEM auxiliary cooling stack is the bottleneck on long pulls. Upgrade the intercoolers before the turbo upgrade, not after.
Supporting hardware
RS4-specific cooling, charge integrity and catch-can housekeeping preserve the wagon utility while supporting the hardware pathway.
Hand-selected hardware that fits the chassis discussed in this article. Confirmed against generation, engine code and regional spec.
