Audi RS4 Avant B7 4.2 V8
The Audi RS4 Avant B7, produced from 2006 to 2008, was one of the most thrilling incarnations of Audi's RS performance brand and arguably the finest high-performance wagon of its generation. Its party trick — a naturally aspirated 4.2-liter V8 that revved to an astonishing 8,250 rpm in an estate car body — created a driving experience that was both wildly exciting and supremely practical.
The engine was the RS4's defining feature. Based on Audi's 4.2-liter V8 but extensively reworked by quattro GmbH, the BNS engine used high-flow cylinder heads, individual throttle bodies, lightweight forged internals, and a specific intake and exhaust system to produce 420 horsepower at 7,800 rpm — an extraordinarily high power peak for a naturally aspirated engine. The specific output of 101 hp per liter was remarkable for a production V8, achieved through engineering finesse rather than forced induction.
The engine's character was defined by its top end. Below 4,000 rpm, the RS4 was deceptively civilized — torquey enough for relaxed driving but not revealing its full potential. Above 4,000 rpm, a transformation occurred. The exhaust note hardened, the engine seemed to find another gear of urgency, and the pull to the 8,250 rpm redline was relentless and intoxicating. This was an engine that rewarded drivers who used every revolution, building drama as the tachometer needle swept past 7,000 and the V8 reached a frenzy that was more Ferrari than Audi.
The quattro all-wheel-drive system used a Torsen center differential with a 40:60 front:rear torque split, providing the traction to exploit the engine's output in all conditions. The six-speed manual gearbox had a precise, short-throw shift action that complemented the engine's character perfectly — there was no automatic or dual-clutch option, reinforcing the RS4's driver-focused ethos.
The DRC (Dynamic Ride Control) suspension system was innovative: hydraulic cross-linked dampers that connected the diagonally opposite corners of the car, reducing body roll during cornering while maintaining ride comfort over bumps. The system was more effective than conventional anti-roll bars and gave the RS4 a remarkably flat, composed feel through corners despite its wagon body style.
The Avant body added approximately 100 kg over the sedan but provided genuine estate car practicality — enough luggage space for a family holiday and the versatility to carry large, awkwardly shaped loads that a sedan simply couldn't accommodate. This combination of supercar-rivaling performance and everyday utility was the RS4 Avant's unique proposition.
The B7 RS4 Avant remains the only RS4 to feature a naturally aspirated engine — subsequent generations have used twin-turbo V6 and V8 configurations that trade the B7's high-rpm character for greater low-end torque and better fuel economy. For enthusiasts who value the drama of a naturally aspirated, high-revving engine, the B7 RS4 Avant represents a unique and irreplaceable driving experience.
The BNS V8 is generally robust but has specific concerns. Check for carbon buildup on intake valves — a common issue with direct injection engines. Listen for timing chain rattle on cold start. Verify that the DRC suspension system is functioning correctly — failed DRC lines cause poor handling and are expensive to repair. Check for front differential CV joint wear. The 6-speed manual gearbox is strong but check shift linkage condition. Inspect the brake system — these are heavy cars with high performance and consume brakes. Check for rust in arches and sills (less common than earlier Audis). Service history documenting regular oil changes is important — the BNS engine benefits from frequent oil changes.
The B7 RS4 was available as sedan, Avant (wagon), and Cabriolet. The BNS 4.2-liter V8 produced 420 hp at 7,800 rpm — the most powerful naturally aspirated Audi V8 in a road car. Only a 6-speed manual was available. The RS4 B7 was the last naturally aspirated RS4 — subsequent B8 and B9 RS4s used twin-turbo engines. Production was handled by quattro GmbH at Neckarsulm.