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2003 Audi S3 - Heavy Hitter

More than three years in the making, this 550hp rear-driven RS4-powered 2003 Audi S3 is knocking heads and taking names.

Justin Fivella
Dec 1, 2006
Photographer: Chris Eckermann
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Maneuvering across the rural countryside, the midnight hatch consumes scenery at an alarming rate. Having dropped into the valley, the car began its ascent up the serpentine stretch of tarmac that exited the canyon. Atop the ridge lay a lookout with a perfect view of the valley and its crooked road - a spot where drivers congregate to watch cars tackle the valley.

The automotive banter comes to a sudden halt as the group of enthusiasts hears the crack of the high-revving V6. Bellowing off the canyon walls, the car's ferocity rivals a racecar as the stubby hatch has made not only short work of the straights, but carves corners like a hot blade in butter. The acoustics intensify as the car makes its way up the road, reaching a crescendo as it powers through the final hairpin.

2019 Audi S3
$44,500 Base Model (MSRP) MPG Fuel Economy

The group of drivers stares in silent disbelief as the Audi exits the sharp corner, overtakes a 911 Carrera and passes them with its tail out, tattooing black stripes into the pavement.

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Make the mistake of underestimating this purpose-built Audi S3 and you too will disappear in its wake, as many Porsches have already done.

Sound like a scene out of a movie? Well, for Markus Oberscheider of O.CT Tuning in Lustenau, Austria, it's just another day behind the wheel of his badass '03 S3. Built with a purpose, Markus laughingly admits his hatch is anything but mundane.

Known for its ECU tuning, O.CT established itself as a formidable tuner before setting out to build an S3 like no other. "When we told people we were going to stuff an RS4 motor into an S3 and make it rear-wheel drive, people doubted us. So we did it to prove we were good enough," Markus asserted.

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And prove it they did. Beneath the hood of the S3 lurks the RS4's 2.7 liter V6 bi-turbo that churns the rear meats via a custom RWD conversion. But like those who underestimated O.CT's ability to build it, don't write this conversion off as something like a Mk2 VR6 swap, or a disconnected Haldex RWD conversion on an R32. This, my friends, is an entirely new car.

After taking measurements, Markus and the crew at O.CT realized there wasn't a shot in hell the six-pot would fit the space provided for the factory four-banger. So like any normal-thinking person, they simply redesigned the engine bay.

According to Markus, the entire firewall was cut, redesigned and repositioned 200mm further back to aid installation and help achieve 50/50 weight distribution. After hanging the motor in the stretched bay, they cut the center of the firewall to make room for the new transmission, and fabricated mounts to keep it in place.

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The center of the floorpan was then removed, along with the rear fender wells. In their place, a new transmission tunnel and inner fenders were fabricated - large enough to accept the new RWD driveshaft, axles, diff and wider rubber. "I had the entire car down to a shell at several different points and modified just about every piece on it," Markus said.Forward motion would now be the responsibility of a straight-cut six-speed Quaife gearbox. It was located in the new tunnel once Markus had fabricated a bellhousing and transmission mounts.

Knowing the car would be pushing a vast amount of power to the rear skins, Marcus looked west to create a bulletproof driveline. He opted for an unbreakable Dana 44 rear end, more typically used in heavy-duty offroad applications. It's hooked up to Corvette ZR1 axles and a custom driveshaft from the V6.

Markus explained that using either the S3 or RS4 quattro setup, or something more substantial, would've moved the engine too far forward and added unwanted weight in the nose. "In order to keep the weight distribution 50/50 the car had to be RWD with the motor as far back as possible," Markus said.

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By this stage, neither the RS4 nor S3 suspension would work. Faced with the problem of redesigning new suspension pieces, Markus didn't bat an eye about fabricating McPherson struts for the front and rear, using "one-off" fully adjustable KW coilovers. He also created a new subframe, lower A-arms, tubular rear control arms and constructed the necessary steering components.

Markus concedes there were easier ways to achieve such a conversion but felt there was no better method. "It would've been easier to graft an A4 front end to the S3 bodyshell. This would have simplified the process of fitting a large, longitudinal V6 motor into a space designed for a small transversal four cylinder. But I wanted everything to fit the S3 bodyshell to keep it compact," said Markus.With everything mounted, the engine was removed and massaged for more power while a complete RS4 wiring harness was fitted. When the bi-turbo was reinstalled it wore larger K04 turbos, a custom intake, piping and the unique FMIC you see in the photos. The car exhales through a custom dual 70mm turbo-back exhaust.

Controlled by the stock RS4 ECU, Markus claims the combination is good for 550hp and over 440 lb/ft on 100 octane RON fuel.

Harnessing the road-rocket, Markus fabricated carriers for the giant 380mm (15") front and 322mm (13") rear rotors, squeezed by dual Porsche calipers on the front and single four-pots on the rear.

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To ensure the stopping power could be fully utilized, the hatch wears an equally gargantuan set of 18" Work Meister three-piece S1 wheels, measuring 8.5" front and 11.5" rear. Wrapping the wide hoops, the car was shod with 235/40 front and 295/30 rear Conti tires that can be spun at will.

Function over form, Markus explained the wide fenders were added purely to get sufficient rubber under the car to corral the 550 prancing ponies.

The bodywork was completed by local bodyshop Color Concepts in a speedy two weeks. They added a stout 60mm (2.5") of extra metal to the front fenders, and 100mm (4") on the rear.

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The wider stance was accentuated by a host of widened pieces, including an RS4-style front bumper, stock rear bumper and skirts. The original silver hue was then ditched in favor of more menacing black paint.

The interior was also stripped and outfitted with a carbon dash, console, door cards and all accompanying pieces. Nestled in the glossy weave is a Stack Racing instrument cluster, along with a three-spoke Sparco wheel. A pair of lightweight Porsche GT3 seats were also utilized, along with a custom rollcage and a rear-mounted fuel cell.After more than three years of sporadic work on this vaunted ride, Markus and the O.CT crew have created an S3 unlike any other; a car so heavily modified you can hardly call it an S3 anymore.

No matter what you call it, call it fast. So heed our words, you have been officially warned to never again judge a book by its cover; for books like this O.CT Audi S3 walk softly, but carry a very big stick.


Markus Oberscheider

Location: Lustenau, Austria

Occupation: Owner of O.CT Tuning

2003 Audi S3

Engine: 2.7 liter bi-turbo RS4 V6 swap with O.CT Tuning software and injectors, larger K04 turbos, custom FMIC and piping, fabricated 70mm dual turbo-back exhaust system, custom intake, aluminum radiator with dual electric fans, rear-mounted battery and fuel cell

Driveline: RWD conversion using Quaife six-speed transmission, custom bellhousing, transmission mounts and driveshaft, Dana 44 rear end inside custom aluminum case, Corvette ZR1 rear axles, Spec stage 3 clutch

Suspension: fabricated McPherson front and rear strut suspension design, tubular control arms, KW coilovers, O.CT front and rear sway bars and strut tower braces

Wheels & tires: 18x8.5" (front) and 18x11.5" (rear) Work Meister S1 three-piece wheels, 235/40-18 (front) and 295/30-18 (rear) ContiSportContact 2 tires

Brakes: 380mm (front) and 322mm (rear) cross-drilled rotors, dual Porsche calipers (front) and single four-piston (rear) on fabricated carriers

Exterior: 60mm (front) and 100mm (rear) widened steel fenders, widened RS4-style front bumper, stock rear bumper and side skirts

Interior: carbon dash, console, steering column, door cards and interior pieces, Sparco 380mm three-spoke steering wheel, Stack Racing instrument cluster with LED gear indicator, Porsche GT3 seats, rollcage, Quaife polyurethane shift knob

Audio/Visual: 550 thundering horses as a soundtrack

By Justin Fivella
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