[2] The current B9 generation is powered by a turbocharged 3.0-litre V6 TFSI engine, with rivals including the BMW M340i xDrive and Mercedes-Benz C450 AMG/Mercedes-AMG C43 4MATIC.

First shown to the public at the May 1991 Barcelona Show, it was designed to replace the outgoing C3-based Audi 200 turbo quattro 20V and retained its five-cylinder engine.

[7][8] Being the first S4 model from Audi, it is commonly referred to as the Ur-S4, derived from the German: Ursprünglich augmentive word (meaning: original).

In line with the switch in model name, Audi temporarily discontinued the use of the S4 name and began selling an updated but fundamentally identical version of the car, based on the "new" A6 and badged as S6.

[1] This powerplant made it rather powerful by contemporary standards, and the vehicle with five-speed manual transmission was able to accelerate from standstill to 100 kilometres per hour (62.1 mph) in 6.2 seconds.

Examples produced June 2001 to end of production are 2002 Model Year cars, the 10th digit of the VIN being the number "2".

In all US-market cars, the engine was detuned to meet US emissions regulations; output was reduced to 184 kW (250 PS; 247 hp) and 350 N⋅m (258 lbf⋅ft) (identification code: APB).

The rear suspension is an unequal length double wishbone design; the lower control arms are mounted to a subframe which also carries the differential housing.

Of note, one of the S4's, racing against true GT cars, even ran as high as second place (in the rain) at Barber Motorsports Park.

This was considerably worse than the earlier V6 models, leading to the addition of a $1,700 gas guzzler tax (combined 20.2 miles per US gallon (11.6 L/100 km; 24.3 mpg‑imp)) for the six-speed manual sedan in the United States.

[1] Replacing the 2.7-litre 'biturbo' V6 engine of the previous generation B5 S4, the new B6 S4 powertrain[1] gained an all-aluminium alloy 4.2-litre, 40 valve (five valves per cylinder) V8 engine (parts code prefix: 079.C, identification code: BBK), with flywheel-end chain-driven double overhead camshafts, roller-finger rocker arm cam followers, and included variable inlet camshaft timing.

It also used a strengthened alloy crankshaft bedplate for the five main bearings, and a two-part baffled oil sump, and a light-alloy variable intake manifold (VIM), containing the fractionally sequentially actuated fuel injectors.

The exhaust system includes vacuum-operated valves in the twin rear silencers (mufflers), finished with chrome plated tail-pipes.

Standard wheels[1] were 'Avus-III' die-cast aluminium alloy, 8.0Jx18H2 ET45 in size, and fitted with 235/40 ZR18 95Y XL (eXtra Load) high performance tyres, with factory supplies being either Continental SportContact2 or Michelin PilotSport PS2.

There are a few mechanical changes, such as revised springs and dampers and, from model year 2007, an updated Torsen T-3 automatically biasing centre differential, featuring a 'default' asymmetric 40:60 front-rear torque split on manual transmission models, along with the later Bosch ESP 8.0 Electronic Stability Programme[1] and gloss black painted brake calipers.

The new trapezoidal single-frame grille, Bi-Xenon high-intensity discharge lamp (HID) headlamps, L-shaped tail-lamps, quad exhaust tail pipes, and discrete V8 badging below the side repeater indicators help distinguish the B7 from the previous B6 model.

Available only in the United States, the exterior has unique front and rear bumpers, a carbon fibre boot lip spoiler and lower front splitter, a rear functional red tow hook, and a high gloss Phantom Black painted grille with the "quattro" emblem.

15-spoke DTM alloy wheels, along with optional dealer-fitted 'Audi four-rings' decals for the front doors complete the exterior makeover.

On the mechanical side, the S4 25quattro was the second Audi, after the B7 RS4 to be fitted with the latest Torsen T-3 asymmetric ATB centre differential for its quattro permanent four-wheel drive system.

The final drive ratios are 3.889.From November 2008, the fourth generation of the 'Audi S4 quattro'[15] (Typ 8K) entered factory production.

Combined with the Sport Rear Differential Audi was able to greatly improve the weight balance and dynamics of the S4 over previous models.

Mechanically, the facelift B8 (known colloquially as the B8.5) was upgraded with electromagnetic steering and a lighter crown gear center differential.

This petrol engine displaces 2,995 cubic centimetres (182.8 cu in), and it is rated by Audi to a power output of 245 kW (333 PS; 329 bhp) from 5,500 to 7,000 rpm.

This high power output is achieved by using forced induction – and specifically, an all-new Eaton 'Twin Vortices Series' (TVS) Roots-type positive displacement compressor.

It is mounted on top of the engine, within the 'Vee', pumping air directly into the inlet manifold, and incorporates two separate water-cooled intercoolers.

However, a comparison in the American automotive magazine Road & Track[25] showed the sprint from 0 to 60 mph (97 km/h) in 4.5 seconds for the 6-speed manual transmission.

[28] This is one of the most important reasons for Audi to downsize their engines, while keeping the output equivalent better, by using forced-induction such as supercharging or turbocharging.

Noticeable changes to the B9 included a modern, more angular exterior, newly designed wheels, and a new turbocharged V6 engine co-developed by Porsche.

LED headlights are standard while a flat-bottomed steering wheel, "S" embossed seats, and quad tailpipes differentiate the S4 from the B9 A4.

[32] In European markets, the facelifted B9 S4 - launched in 2019 - is now powered by a 3.0-litre turbocharged diesel V6 with 347 PS (255 kW; 342 hp) and 700 N⋅m (516 lbf⋅ft), mated to a ZF 8-speed torque converter automatic gearbox and all-wheel-drive.