July 10, 2005

Project Audi B6 S4: Performance Tuning
Text & Photos by Jason Teller

Project B6 S4 came to a serious crossroads earlier this year. It was the dead of winter, a rather cold and difficult winter compared to recent ones, and we began pondering what the car's future would hold. With B7 S4's, including their single-frame grille (which we actually like) and a host of other improvements scheduled to hit the market in a mere few months we actually considered putting the red B6 S4 out to pasture.

The other option, of course, was to contemplate all the potential aftermarket improvements that might be made thus inducing a euphoric to-be-tuned-in-the-future calming effect. It was about that time that we firmed up plans to pursue a serious tuning program with this vehicle.

Interestingly it would be a totally different set of expectations and possibilities that would govern the way we upgraded our B6 S4 when compared to the aftermarket tuning of our previous generation B5 S4. No longer having the brilliant bi-turbo engine to play with, we would now be trying to coax a little additional performance out of the solid 4.2-liter, naturally aspirated powerplant.

Owners of the aforementioned B5 S4 probably turn to chip tuning first and foremost for quick power upgrades. Chipping the B6 S4 yields no such windfall of power, but can provide some other advantages.

ECU Upgrade

When it came time to improve the programming in our project car we turned to the folks at Stratmosphere with their O.CT tuning program. O.CT, short for Oberscheider Chip Tuning, refers to the Austrian tuning company managed by Markus Oberscheider. Stratmosphere has formed an exclusive partnership with O.CT and together they have been releasing fully-tested, timed-to-market Audi and VW upgrades to the North American marketplace since 2002.


There are two types of chip upgrades for the B6 S4 on the market. One group - from tuners such as Revo, GIAC and APR - are ECU "flashes". That essentially means that the ECU stays installed in the car and the upgrade is performed via the vehicle's OBD-II port. The upside is that the ECU case does not have to be cracked (Audi has made it much more difficult in this vehicle to access the ECU), but the downside is that a VAG tool may be able to overwrite the programming in certain situations.

A second group of tuners - O.CT, AMD and Neuspeed - actually solder directly onto the ECU itself. This of course requires that the ECU be removed from the car. As mentioned this can be a challenging task, although the upside is that the programming cannot and will not be subsequently overwritten. Owners debate whether either methodology is less likely to be noticed by a dealer servicing a chipped vehicle and we're not actually going to comment on that. We think it's fair to say that if you are making performance modifications to your vehicle then it is more than likely that any dealer or shop (or Audi field representative for that matter) will be able to tell.

Based on O.CT's reputation and the performance chacteristics of their B6 S4 chip programming we were quite comfortable allowing them to solder onto our ECU. Once back into the car it was only a matter of a few quick confirmation checks via an attached VAG tool and the upgrade was complete.

We did not dyno Project B6 S4 before or after to confirm O.CT's power upgrade claims, however as previously stated there was little expectation that chipping alone would result in an appreciable pick up of power. Instead the rationale behind the chip upgrade had more to do with engine management itself.

According to our research, including our first S4 Shootout, the O.CT chip upgrade produces a fairly flat torque curve with great torque at relatively low rpm's (between 3300-3700). This results in a feeling of greater throttle response relative to stock, as well as better throttle response during shifts. The aftermarket programming also bumps the vehicle's redline up from 7250 to 7500 and removes the top speed limiter altogether.


Milltek Downpipes, Cats and Cat-back Exhaust

Of course we never drove the car with just the ECU upgrade because that same day we also installed a myriad of other performance-related upgrades available through Stratmosphere - a Milltek dual stainless steel cat-back exhaust system (resonated), Milltek downpipes and cats and Strat's own HyperFlow induction system. Stratmosphere and O.CT in fact recommend an exhaust system upgrade in conjunction with the ECU upgrade in order to realize maximum results.

We had previous experience with Milltek from our B5 S4 and were so satisfied that it would have been difficult not to come back for a second helping. It is the design of any aftermarket exhaust which defines its overall merit since the design will ultimately characterize the fit and finish of the system (how it fits and how it looks), the performance (what gains it can produce) and the exhaust tone (how it sounds). The interworking of these items, plus the additional factor of price, are all important considerations.

This is precisely why we like Milltek so much. Fit for the exhaust was spot on - so good in fact that the tips were perfectly spaced and positioned from the get-go with no further adjustment required once the car was lowered. The tips themselves are clearly differentiated from stock, yet are not so large that they defile the generally refined look of the S4.

From a performance point of view we went with the full manifold-back system in order to get the best flow possible through the system. The stock B6 S4 exhaust is known to be notoriously restricted and, as previously mentioned, the combination of chip tuning and exhaust upgrades work very well together.

A typical Audi catalytic converter has somewhere around 400-500 cells per square inch (cpsi) and restricts airflow because there is less open area. The Milltek Hiflow cat is fully integrated with a larger bore downpipe and has only 200 cpsi - much more open area resulting in reduced back pressure and increased flow. Emissions levels are comparable to stock despite the fact that the primary cats have been replaced and the secondary cats have been removed altogether. The downpipes and cats are smaller and weigh less, another performance consideration.

The final test - exhaust tone - is where the Milltek really shines in our opinion. Although we chose the resonated version in an attempt to keep things relatively civilized we have still been overjoyed with the sound of the system. First and foremost we can hear ourselves accelerate and we get a very satisfying blurp when we go wide open throttle. Next, we can now hear the exhaust tone at idle and it has just the slightest menacing attitude to it - in a good way. The S4 for all its greatness is just too polite in stock form. The exhaust upgrade allows us to finally hear (and feel) the rumble of the big V8 under the hood!

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