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Polished S4

Polished performance from a subtly modified Audi S4

Words by Michael Knowling, Pix by Julian Edgar

Click on pics to view larger images

At a glance...

  • Rare (in Australia) Audi S4 bi-turbo
  • Subtle exhaust, management and suspension mods
  • Shining on-road performance and stability
  • Plenty of further tuning potential!
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This article was first published in 2006.

Peter Fitzgerald’s Audi S4 is one of the best modified street cars we’re ever driven.

Forget talking about huge, inaccessible power figures. The tweaked Audi bi-turbo is on boost the moment you breathe on the throttle; its real-world performance is scorching. Don't bother watching the tacho - just nail it and go!

The re-valved suspension gives a refreshingly comfortable ride – completely in keeping with the luxury feel of the car. The free-flow exhaust system is quiet and free of annoying drones. The quattro all-paw drive and electronic stability control add to the feeling of comfort and security.

Our only dislike was the heavy action of the short-shift mechanism. Mr Fitzgerald answers this by pointing out you can easily reduce the number of gear shifts. He suggests shifting from first to third to fifth gear - and the engine sure as hell has enough torque to do it...

Rewind to 1999 for a moment. The Audi S4 was released in Australia featuring quattro four-wheel-drive and a new five-valves-per-cylinder 2.7-litre V6 with twin turbochargers. With its 195kW and 400Nm from 1850 to 3600 rpm, the ’99 S4 was hailed one of the most rapid saloons in the world – claimed 0 – 100 km/h was 5.6 seconds.

The only problem was the AUD$113,800 price of admission.

Today, the Audi S4 bi-turbo is still regarded as a genuine performance saloon – the biggest difference is you can pick up a second-hand model from around AUD$60,000. And now that it’s out of factory warranty, there’s nothing to stop you tweaking it for even more speed; that bi-turbo engine is waiting to be unleashed!

Peter Fitzgerald, one of Australia’s most awarded drivers of the last 25 years, is one of the few people to recognise the potential of the twin-blown Audi.

Click for larger image

“I bought the S4 as a road car because I had owned a Merc CLK430 and BMW 540i and I was used to having a bit of punch.

“I researched the S4 and, after taking some for test drives, I was quite impressed.

“The Audi also had the Euro heritage and feel to it. It was a little bit unique,” Mr Fitzgerald says.

But, after purchasing a discounted example with a few cosmetic scratches, the standard performance of the S4 soon dulled.

“I know that Audi claim 5.6 seconds 0 to 100, but with 195kW and 1600kg I think that’s a bit optimistic. To me, it didn’t feel that quick – it wasn’t super outstanding - but it did have the torque to make it really nice to drive in the city.”

At this point, Mr Fitzgerald turned his attention to modification - and the first step was to obtain a baseline power figure. In stock form, power at the wheels was 117kW (measured on a Dyno Dynamics AWD chassis dyno).

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The first upgrade was the fitment of a Remus cat-back stainless exhaust. According to Mr Fitzgerald, the Remus system gave a good power gain (about 13kW at the wheels) but failed to deliver the note he was chasing. He later added a Miltec front section of exhaust which bolts to the back of the turbos and includes a 100 cell stainless cat converter. Mr Fitzgerald fabricated a joiner section to mate the Miltec and Remus systems.

Meanwhile, the air intake had also been upgraded. Mr Fitzgerald fitted an Evo Motorsport cold air kit and revised the plumbing to deliver the most consistent intake temperatures possible. Using a digital temperature probe, Mr Fitzgerald has measured intake temperatures that rarely rise 5 degrees Celsius above ambient. A conical air filter was also installed as part of the upgrade.

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After being treated to its free-flow exhaust and cold air intake, the V6 engine spat a water pump – according to Mr Fitzgerald, a common problem. So, while repairs were being carried out, the opportunity was taken to replace the standard crank-driven cooling fan with an electric thermo fan. This might help achieve slightly more power.

An ECU tune was next on the agenda but dyno testing at this time showed there was something amiss in the Audi’s engine bay. Fault-finding revealed some deteriorated boost/vacuum hoses and a broken airflow meter. Once these were replaced, PowerChip retuned the factory ECU to deliver a fat torque increase across the rev range.

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This graph shows the current output (plotted in dark blue) reaching 174kW at the wheels. The pink plots show the output when there were problems with the airflow meter and under-bonnet hoses. In total, the changes to Mr Fitzgerald’s S4 have achieved around 40 percent more power. Flywheel output is estimated at around 260 – 270kW.

But this car isn’t all about power.

Handling is improved with the fitment of aftermarket suspension and wheels. A set of H&R replacement struts were fitted but these have since been re-valved to deliver a more comfortable ride. Mr Fitzgerald says the suspension is around 10 – 20 percent stiffer than the factory-tweaked Audi RS4. The standard wheels have also stepped aside for 18 inch BSA alloys wearing Falken tyres. These are left-over wet weather race tyres.

Click for larger image

In standard form, the S4 has plenty of visual bling – just look at its high-fashion aluminium mirrors – but Mr Fitzgerald’s example has some extra eye-catching appeal. The big wheels, lowered stance, Remus exhaust tips and tinted windows are all that’s needed. A respray has also eliminated the scratches caused by the previous owner.

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Inside, the S4 comes with leather Recaro seats, full instrumentation and equipment. Mr Fitzgerald’s example is fitted with black trim - other examples he drove had a light colour trim which showed more signs of wear. The only interior change is an Evo Motorsport short-shift.

At present, Peter is considering fitting a RS4 body kit (which will mean hacking off part of the rear bumper), RS4-type turbochargers, improved intercoolers and bigger injectors. There’s immense potential - 300kW seems like a pretty achievable goal... And all in a car that one of the sweetest we've ever driven!


Fitzgerald Racing Services
+61 3 9897 1555

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