The S4 is a venomous cara proverbial wolf in sheeps clothing. With the mild-mannered outward appearance of a slightly lowered A4 sporting 17-inch wheels and a deeper front bumper, only those that can decipher the subtle badging know what lies beneath. The 2.7L 30-valve, DOHC, twin-turbo V-6 engine that lies in the heart of the beast may be one of the most under-powered 250 hp and 258 lb-ft engines the world has ever seen. Not to say that it doesnt have oomph. Hell, it can take out most other mid-priced compact luxury sedans on the road, thanks to the all-wheel drive and turbo power, but the engine is capable of so much more.
In Germany, and other parts of Europe, the RS4 is the ultimate incarnation of the S4. Built on the A4 Avant platform, the motor pumps out 380 hp and 325 lb-ft and shares the same basic structure as the S4s bi-turbo V-6. Though there are hardware differences between the S4 and RS4 enginesa specially cast and reinforced block, larger turbos, and a freer-flowing exhaustit is a factory-produced model with emissions restrictions and warranty terms to meet. There are also other reasons why the S4 doesnt produce as much power as the engine is capable of.
In the American market for the 2001 model year, Audi priced the S4 at $38,900 new. The A6 also comes equipped with the 2.7T engine for a similarly priced $39,500, while its 4.2L V-8 makes 300 hp and 295 lb-ft and sells for $49,400. Interestingly, the mid-sized A6, equipped with the 2.7L bi-turbo motor and Tiptronic transmission, sprints to 60 mph 0.1 seconds quicker than the Tiptronic 4.2. The A8 is the next step up and is a full-sized sedan. It comes with the same V-8 as the A6 but produces 310 hp and 302 lb-ft for a whopping price tag of $62,200. The S model of the A8 is priced even higher at $72,500 and comes with a tuned 4.2L V-8 producing 360 hp and 317 lb-ft. Granted, were only talking engine figures here and not taking into account all of the other features that each model presents. But whats the reason that Audi just doesnt turn up the boost on the S4 and have it produce 300 hp and 310 lb-ft of torque? Simple. Who would pay $49,400 for a car that produces the same power as one that costs $39,500, or $62,200 for one that only produces only 10 hp more? Audi wouldnt be able to compete with its own product.
Whatever the reason may be, the S4s bi-turbo engine isnt being used to its full capacity. Thats where the automotive aftermarket comes in. With all the performance parts available for the S4, the car can be made to out-perform almost anything on the road (Barring multi-kilo-dollar super cars and cars with engines featuring three times the displacement.MAX) and still look good with luxury car comfort to boot. The question is where to start. Audi tuners have plenty of experience with the 1.8T, giving them the perfect background for modification of the 2.7T. The Bosch Motronic engine management system, which controls both the 1.8T and 2.7T, allows for easy modification of the fuel, boost, and timing curves. This gives an experienced tuner the ability to extract huge amounts of power with minimal impact on fuel economy and drivability.
Audi Performance and Racing is more than just a tuner, its an engineering firm. Well-known in the Audi community, APR has been tinkering with the 1.8T since its introduction to the States. APR has performed extensive research on the 1.8T and developed a 310 hp upgrade kit that replaces a good part of the forced induction system and more than doubles the stock 1.8Ts power, all the while keeping the car streetable and reliable. Currently, APR is working on applying that technology to the transversely mounted 1.8Ts that are being put into the VW Golf and Jetta, as well as the Audi TT. When Audi told the world that the S4 would be coming to the States, APR was first on the list. As soon as the car arrived, it was torn apart so that APR could start developing parts for it. APRs prototype S4 (As featured way back in our February 2000 issue.MAX) has given way to awesome products for anyone looking for surreal performance.
APR is located in Auburn, Alabama, probably one of the last places youd think to look for a premier Audi/ Volkswagen product developer. With a staff of electrical, mechanical, and physics engineers, as well as downright smart people, its no surprise that they developed the Enhanced Modular Chipping System (EMCS.MAX) for the new drive-by-wire cars. EMCS allows the user to switch between different ECU programs using the cruise control stalk. Using EMCS exclusively in its chip upgrades since June 2000, APR offers all of its customers flexibility when it comes to engine performance. In order to better understand EMCS, we contacted Brett and Frank at APRthe men behind the system.
Brett explained to us that EMCS was developed in response to customers requests for a switchable chip. Based on many years of experience with electrical circuitry, they knew it was possible to make this available, but that it would have to be done through the software, rather than the hardware, for the sake of reliability. So rather than reprogramming the EEPROM chip, adding a switchable socket with a couple of slots, and putting more chips in those slots so that the program could be changed with a cabin-mounted switch, he and his coworkers developed a different approach. APR decided that a separate circuit, in the form of a daughterboard, soldered in place of the EEPROM would perform the different functions that APRs engineers required. The daughterboard, which consists of a four-layer printed circuit board and associated circuitry, mimics the function of the memory device it replaces (The EEPROM.MAX), while integrating a number of EMCS-specific features.
Since the daughterboard has a large amount of read-only memory, several engine programs can be put on the board as well as all other necessary software to allow the programs to be switched. Since the cruise control stalk is directly linked to the ECU, and is one of the lesser-used electronic systems in the vehicle, APR decided to contract it as the link between the cockpit and the ECU.
Consider switching between stock, high performance, 100-octane, and valet programs; locking these programs with a security code so that they cannot be changed by others; as well as performing throttle body alignments and erasing engine-fault codes, without the need of the VAG computer. Also, it means that if APR updates its software, its customers can simply call APR and get the new program e-mailed to them, rather than having to send the ECU to APR for the update. Also, if the customer decides to add additional engine management programs to his ECU, or if he decides to upgrade to a higher stage, he can do so with minimal down time. And lets not forget possibly the best feature of APRs chip: It is completely undetectable, even by dealerships diagnostic tools (But we didnt tell you that.MAX).
The S4 that we tested APRs equipment on is an Imola Yellow 2000 model owned by Brian Konoske. Brian was intrigued by the design and features of APRs EMCS and decided to get the Stage 1 kit, along with a K&N replacement filter. First stop was Under Pressure Research and Development in Huntington Beach, California. The S4 was pulled on the dyno, strapped down, and spun. The S4 produced a maximum horsepower of 165.3, and a maximum torque of 194.4 to the wheels.
With baseline numbers from UPRD, the ECU was pulled and then sent to APR. Brian ordered all that APR offers with its EMCS, including the stock, performance, valet, and race engine management programs, the security lockout feature, and the throttle body alignment/fault code erase bundle program.
For the stock program, APR simply copies the original management code to the EMCS ROM. The performance program is what APR sends with every EMCS that it sells. The performance program raises maximum boost to 1 bar/14.7 psi, advances timing to optimum levels along the entire rev range for 91 octane gasoline, remaps the fuel curve to compensate for the boost increase and timing advance, and also improves throttle response. The boost increase places the turbos at the peak of their operating efficiency but does not overtax them.
The valet program is an added safety feature. Basically, if the engine isnt being asked to accelerate the cars mass quickly, the ECU dials back fuel, boost, and timing to save gas and the engine from unnecessary wear. APRs valet program changes the maximum load level to about 50 percent of the stock program, limiting air flow to 50 percent of stock, resulting in acceleration that borders on heinous. The race program is equally innovative.
In a turbo application, it makes sense to add more boost pressure and to increase the fuel accordingly, if you want to increase the power. However, when you try to get too much boost out of a turbo, it can shorten the life of the turbo. Since APR designed its performance program to make use out of the turbos maximum efficiency, the company also wanted to design a race program that wouldnt require more boost but would make more power.
One of the tables that exists in the ECU programming is the minimum advance for best torque, or MBT table. The MBT is used to determine the engines deviation from ideal values. When compared with actual timing values, the MBT values are higher due to the octane value used in actual timing. By using 100-octane fuel as the fuel value, APR is able to program the base ignition timing much closer to the MBT values, increasing horsepower considerably. However, 100-octane must be used, as the knock-sensor timing routines that prevent detonation only allow the ECU to adjust for a two to three octane deficiency.
The security lockout feature is fairly straightforward. When you order your EMCS, you can provide APR with a one- to four-digit security code that prevents anyone who doesnt know the code from changing the program settings. The code must be input using the cruise control stalk before any changes can be made. The throttle body alignment feature/ fault code erase can be useful if you either need to reset the throttle bodys butterfly plate due to a new modification, or if you have a pesky check engine light that continues to stare at you, even after you have corrected whatever problem caused it. One of the most common reasons for the check engine light to come on is that the throttle body boot on earlier S4 models has a habit of tearing. This can be especially frustrating in high- horsepower S4s (APR has a boot in production that is extremely durable and does away with this problem.MAX).
Once the modified ECU was in the vehicle, we took it to UPRD again. This time the S4 laid down 206.7 hp and 268.3 lb-ft at the wheels, a 41.4 wheel hp and 73.9 lb-ft increasequite impressive for little more than the addition of a filter and chip. Because UPRD is presently the only facility with an all-wheel-drive chassis dyno that is publicly available, it is constantly in demand, thus we were only able to run the car in performance mode due to time constraints. Brian, though quite happy with the power increase, wanted more, and for that, he looked to APR for some exhaust work. APR was nearing the end of the redesign process of its after-turbo exhaust, in order to improve flow and also to quiet it down for those that desired to keep their S4s a little more highway-friendly. Constructed completely of stainless steel, it replaces the downpipes, catalytic converters, midpipe, resonator, and muffler. Brian was so eager to get the exhaust on the car that he drove it out to one of APRs installation facilities in Arizona to have the exhaust installed once it was ready.
During the vehicles stay in Arizona, Brian had APR send out one of its PC- interface EMCS reprogrammer boxes, as well as e-mail him the updated performance and race programs so he could reprogram the ECU that he had taken home with him. Once the exhaust was installed, he headed back out to the Arizona facility with ECU in hand. Again, it was time to head out to UPRD to find out what the latest round of modification had the car producing. Once on the rollers, the car revved happily all the way to redline, pulling 228.2 hp and 293.9 lb-ft, an increase of 21.5 hp and 25.6 lb-ft. After all was said and done, the total horsepower gain was 62.9 hp at the wheels and about 100 hp at the flywheel, with total torque increase of 99.5 lb-ft and about 150 lb-ft at the flywheel.
APRs tuning expertise shows. With a chip, after-turbo exhaust, and intake filter, the company is able to increase engine output by 40 percent. Now this S4 is truly a wolf in sheeps clothing.