The B7 generation of Audi RS4 was one of the most eagerly awaited cars of its decade. There had been a five year gap between the previous RS4 as Audi didn't build a hot model based on the B6 so, when the 4.2-litre V8-powered B7 was first shown by Audi at the beginning of 2005, anticipation was high. When the car went on sale in 2006, that anticipation turned into unanimous admiration. Finally, the BMW M3 had a serious rival from Audi.
At the heart of the RS4, which was offered in saloon, Avant estate and cabriolet forms, was an all aluminium 4.2-litre V8 with 100hp per litre on the nose. The 420hp motor came with a high 12.5:1 compression ratio and revved all the way to 8,250rpm through a six-speed manual gearbox.
Helping the RS4 handle was Audi's quattro all-wheel drive system, but the German firm also designed the V8 to be as compact as possible.
With clever packaging, the engine's overhang in front of the transmission was greatly reduced compared to previous RS4 models and this made the B7 handle and steer with incredible precision. Power was divided 40/60 front to rear, so the RS4 behaved much more like a rear-drive car when pushed to its considerable limits.
With plenty of traction, the RS4 saloon covered 0-62mph in 4.8 seconds, with the Avant and Cabriolet managing the same sprint in 4.9 seconds. Audi also provided Dynamic Ride Control to reduce pitch and roll at the touch of a button but still provide a compliant ride when not switched on.
In 2008, production of the B7 RS4 came to a close, with sales of the saloon and Avant even at around 1,500 units, plus approximately 500 Cabriolets. Although the Cabriolet was the most expensive version of the B7 RS4, costing £59,580 when launched, it's now no more expensive than either the saloon or estate. Prices for a B7 RS4 start at around £16,000 and rise to £30,000 for the best examples.
ENGINE & GEARBOX
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.
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.
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.
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.
CHASSIS
The steel monocoque of the B7 RS4 comes in saloon, Avant estate and Cabriolet forms and all share the same suspension layout. At the front, there are upper and lower magnesium control arms with hollow anti-roll bar, coil springs and gas shock absorbers. At the back, a multi-link set up uses coils springs, shock absorbers and anti-roll bar. This set-up lowered the RS4 by 30mm compared to a standard B7 A4, while the optional Sport suspension further lowered the RS4 by another 10mm. Not all owners are keen on the Sport suspension as they feel it makes the ride too harsh.
The RS4 suspension design gave a 37mm wider track at the front than the S4 and 47mm of extra width at the back. Filling the wheelarches are 18-inch five-spoke wheels as standard, though it's more likely you will find an RS4 with the optional 19-inch double seven-spoke alloys.
Behind the wheels are floating ventilated and cross-drilled discs of 365mm diameter up front and 324mm at the rear. Audi incorporated extra brake cooling for the RS4 with NACA ducts underneath the front bumper. ABS anti-lock brakes are standard, as is a two-stage ESP system where the ASR anti-skid regulation could be switched off but with stability still active or the whole ESP system could be disabled.
Steering is by a servotronic set-up with hydraulic assistance and fewer turns from lock to lock for the RS4 than other A4 models to give a more direct feel and quicker responses. Audi fitted its Dynamic Ride Control (DRC) system to the RS4 and this has been known to cause problems. The individual DRC shock absorbers are linked diagonally to each other to reduce roll and pitch in corners without compromising the ride quality.
It works very well but the shock absorbers can fail when their seals wear out. This allows the shocks to lose their pressure, which means either new seals or a complete new unit. Specialist tools are needed to replace the DRC shocks and to repressurise the system.
The DRC system can fail without any warning, but listen out for a knocking noise from the suspension that indicates the DRC's main valve has failed. To replace each shock absorber will cost around £300 per corner. Some owners have reverted to a standard coil spring and damper set-up to do away with the DRC system, but most owners prefer the car with DRC due to its impressive handling ability.
Any other knocks or clonks from the suspension will most likely be a worn front control arm, which will be audible when the steering is on full lock. This fault usually manifests itself at around 40,000-mile intervals.
The RS4 came with Pirelli P-Zero tyres from the factory and many owners have stuck with them as replacements, though others report good things about Bridgestones and Vredesteins. For winter use, Vredestein Wintrac tyres are highly rated by owners who use their cars year round. The tyre pressure monitoring system can fail and it means replacing the battery in the tyre valve. They tend to stop working after around five years.
Brakes are one of the RS4's key strengths and the car will stop hard and fast repeatedly on standard discs and pads. However, they are expensive to replace, with Audi dealers charging as much as £2,000 for a full set fitted. This is why many owners are now using EBC or Pagid pads for even better brake feel and lower costs.
LOBA Motorsport offers an uprated front disc brake conversion for around £1,100 that saves 3.36kg from each front wheel assembly. The discs are 3mm smaller than the standard 365mm discs but owners report improved stopping power and less fade during track day use.
Audi offered its own carbon ceramic brake upgrade as an option for the RS4, but it's rare to find a car fitted with this. More likely is to find an RS4 with brake judder caused by a build-up of brake dust on the disc. It's straightforward to have the discs skimmed to cure this problem.
BODYWORK
The steel shell of the B7 RS4 comes with an aluminium bonnet and front wings to save weight. The front and rear wings are flared to cover the wider track of the car and are unique to the RS4. Other distinguishing features are the two large air intakes in the front bumper, with vents behind that help channel are to the two auxiliary radiators positioned behind them.
Part of the appeal of the B7 RS4 is its understated styling, but also the compact dimensions of 4586mm, 1816mm width and 1441mm height make it ideal for UK roads. As for choosing between saloon, estate or cabriolet, it comes down to personal taste, but contemporary road tests and present-day experience shows the Cabriolet is marred by scuttle shake and body flex where the saloon and Avant are impressively rigid.
The cabriolet's fabric roof is electrically operated and folds away in 21 seconds. It can be raised or lowered at speeds of up to 19mph and has a heated glass rear screen. Pop-up roll-over bars extend from behind the rear headrests if the car detects it is about to tip over.
Corrosion simply isn't an issue with any RS4 that has been cared for, but look for poor accident damage or dings to the soft aluminium front wings. However, it's worth checking the door bottoms for signs of paint bubbling that can be easily sorted. Also look for stone chips on the front as the RS4 seems particularly prone to this, though many owners are fastidious and will have had the front resprayed, so make sure the colour match is perfect.
You may find some rust around the battery, which is located in the boot due to space restrictions under the bonnet. This is a known problem to Audi, which recalled affected cars to cure the fault. It's also worth checking for water in the boot of the Avant as the tailgate seals can fail and cost £200 to replace.
Audi fitted bi-xenon headlights as standard with directional beams, which owners say is very useful and effective. Also standard are rear parking sensors and door mirrors with the trademark RS aluminium finish, but make sure these are present as they are attractive to thieves. Electrically folding door mirrors were an optional extra, as was the Optics Pack that brought a black front grille, all exterior trim and roof rails on the Avant.
INTERIOR
The RS4's cabin is very well appointed as standard, with all models featuring leather upholstery, air conditioning, CD stereo and Audi's usual high standards of build quality. In the saloon and Avant RS4 models, sports bucket seats are standard but the Cabriolet came with sports seat similar to the S4's. However, the Recaro bucket seats were an option for the Cabrio.
When the Sport button is pressed, the side bolsters of the sports bucket seats inflate to hold the driver more securely in place. However, this can make the seats too snug for larger drivers and not everyone likes this feature. The Sport button is usually positioned on the steering wheel, but with the optional multi-function steering wheel this button is moved to the dash.
The flat-bottomed steering wheel is a defining RS4 feature and has an aluminium-effect plastic lower portion. A carbon fibre-effect finish was an option.
Other options were included in the Tech pack that brought auto dipping mirrors, auto wipers and a BOSE stereo upgrade, while the Comfort pack included cruise control and heated seats. Satellite navigation was another option and, while it seems dated by modern standard, still works well. However, it cannot accept seven digit postcodes.
Audi's MMI (multimedia interface) is positioned on the dash, so it's not quite as intuitively placed as modern Audi models' but it's simple to use. The rest of the dash is typical of Audis of this age, so it's logically laid out. Check the centre armrest's catch works as it can break.
Look for wear on the outside bolsters of the seats, especially the Recaro sports buckets as they are very prone to rubbing as the driver gets in and out. The optional Recaro seats steal even more space from rear seat passengers, so consider this if you need to carry more than one passenger regularly. The Avant's boot is also not the biggest by any standards so an RS6 Avant might be better suited to family use.
There are Isofix child seat mounts in the rear seats and the saloon Avant come with front, side and curtain airbags. The Cabrio doesn't have curtain airbags but does have deployable roll-over bars in the event of an accident.
Moving the battery to the boot of the RS4, which means there's no space for a spare wheel. In its place is a can of tyre sealant, so make sure this is full as otherwise you could be left stranded at the side of the road with a puncture.
[Big thanks to Sam Collyer for supplying the RS4 seen in the photos. Pictures: MaxEarey]
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