The all-aluminium 4,163cc V8 engine of the B7 RS4 has a bore and stroke of 84.5 x 92.8mm, with a maximum power of 420hp developed at a heady 7,800rpm. Peak revs are 8,250rpm, while maximum torque of 317lb ft arrives at 5,500rpm. However, 90 per cent of peak torque is on offer from 2,250 to 7,600rpm to make the RS4 very flexible in gear.
Subtle looks cloak ferocious powertrain
Audi claimed its FSI (fuel stratified injection) gave better combustion, though 20.4mpg average economy and 324g/km of carbon dioxide emissions are quite hefty for a four-door saloon or estate. Still, the upside is the V8's superb sound and performance, aided by the engine being normally aspirated, so there are no turbos to muffle the motor's noise.
This was Audi's first attempt at a high-revving V8 engine and it found its way into the R8 not long after. Audi was also obsessed by making the engine compact, so all of the ancillaries except the alternator are driven by chains. Compared to the 344hp 4.2 V8 of the contemporary S4, the RS4's engine had modified pistons and conrods, a new crankshaft and bearings plus new cylinder heads to achieve its 420hp. A dual-branch exhaust with larger downpipes was also fitted to cope with the great flow from the engine.
A short-shift six-speed manual gearbox was the only choice for the whole of the RS4's life and across all three body styles. A Sport button sharpens the throttle response by altering the engine mapping.
8,250rpm redline makes for an exciting engine
Audi's quattro permanent four-wheel drive system was a newly developed system for the RS4 saloon and featured and has an asymmetric and dynamic torque split that sends 40% of the engine's power to the front wheels and the remaining 60% to the back wheels. A self-locking centre differential was also included to maintain traction even when one or more of the wheels had lost grip.
The six-speed manual gearbox has proven to be fault-free in the RS4, but make sure the cruise control works properly as there's a known problem with the clutch switch. When it fails, the engine revs don't drop when the throttle pedal is released and the cruise control stops working. The replacement switch costs £23, but an Audi main dealer will charge around £150 to carry out this 10 minute job.
The only problems with the engine itself are both to do with a lumpy idle. Early B7 RS4s suffered from this and Audi solved it with an upgraded ECU fitted under warranty. More serious for a used car buyer is an engine that runs roughly now as it indicates a build-up of carbon deposits inside the engine. Cars that have been regularly driven hard are much less prone to this as high revs clear out the carbon that builds up. A car living in a city may be more likely to suffer this and it can cost up to £1,000 to have the engine professionally decoked.
Milltek exhausts a popular mod for RS4s
Look for debris, such as leaves, cluttering up the radiators as this causes corrosion and stops the radiators working as effectively as they should. Replacement auxiliary radiators will set you back around £500 including fitting. Also look at the pipes attached to the oil cooler. These corrode as the pipes are steel and the cooler is made from aluminium. Specialists can replace the pipes on their own, but in the worst cases you will need to replace the pipes and cooler.
The engine uses more oil than you might expect and some owners report topping up with two or three litres every 1,000 miles, though this does depend on how hard the car is driven. Even with hard driving, the clutch should last 40,000 miles.
Many owners fit an aftermarket exhaust, with the most common choice from Milltek. A complete system will cost around £2,000 fully fitted. Some uprated exhausts will require an ECU remap, which is also another popular modification among RS4 owners. DMS and MRC are the most often fitted uprated ECUs to B7 RS4s and offer small gains in power and torque, but more importantly give a crisper throttle response.
PHer's view:
It's incredibly quick, handles brilliantly and sounds fantastic. The V8 engine is the charismatic heart of the car, free revving with a reasonable torque spread and a glorious sound - a complex mechanical whine from the unit itself and a loud base - heavy throbbing from the exhaust. The gear change is light and slick with an easy clutch action.
Chris Warne
