For many people, modifying and customizing vehicles can be a fun and rewarding experience. Unfortunately when it comes to European cars, it's also a pricey endeavor. That's ok...that just means it takes a little longer. I have only begun to customize my car in order to go, stop, look, and feel better. In every modification I will attempt to improve the performance of the car without compromising the overall character of the S4. For the complete modification list, scroll down to the bottom of this page.
 Yep, I got some new lungs for the beast. You're looking at KKK K16/K04 turbochargers with ceramic coated hot sides and ported/polished housings. The compressor wheel is the same wheel used in the Porsche 911 turbo. They have flow capability to over 550 horsepower. Because they utilize a K04 housing, they bolt right up to the factory manifolds in the factory location. Here you can see a comparison of compressor wheel sizes between OEM stock K03 turbochargers, RS6 K04 turbochargers, and K16 hybrid turbos. The housings must be CNC machined to fit the larger wheel. These turbos can be custom built to serve your application. Email Jacob Buehn (Imolavirus@msn.com) for more info.
Turbo Pic (1) Turbo Pic (2) Turbo Pic (3) Turbo Pic (4)
 The flow capacity of the K16 turbochargers far exceeds the capability of the stock fueling system. In order to maximize the output of the turbos and maintain safe air/fuel ratios, I have installed an upgraded metering and fueling system. Special thanks go out to Mike Shimon (affectionately known as Mr. Piggie in Audi circles) for allowing my car to be a testbed for his new system. The basis of this fueling kit is larger fuel injectors, larger MAF housing and intake plumbing, fuel rail hardware, 5 bar fuel pressure regulator, manual boost controller, throttle cut defender circuit (MAP clamp) and GIAC K03 software which I already had. This fueling kit has headroom to support over 530 hp. It also costs significantly less than the competitor's fueling kits and can be custom tuned to your application. So far I have been very impressed with the capabilities of this kit. The performace of the car is absolutely amazing. At 25 psi tapering to 22-23 psi at redline, engine output should be in the neighborhood of 500 horsepower and 500 ft-lbs of torque. It's enough to pull on my friend's 2003 Porsche 911 Turbo. On the German Autobahns, the car pulls very strongly to 180 mph and beyond.
Contact Mike at www.VASTperformance.com for more info on this fueling kit.
 With the amount of power the S4 now has, good brakes are a serious concern. Living in Germany, I see speeds well in excess of 120 mph on nearly a daily basis. The Stock HP2 brakes work well during most normal driving, but leave much to be desired when braking from 150+ mph. I also would not trust them for race track duty. My solution is the 6 piston Brembo/Porsche Stage IV kit from ECS tuning. For me, this provides the optimal solution as the vast majority of my driving is high speed on public roads. I wanted a big brake kit that will offer strong performance during normal driving and enough reserve for occasional track useage. The ECS Stage IV kit fits the bill. The calipers are HUGE (larger than bread loafs!) and the rotors are two piece, floating, with a diameter of 352 mm. The ECS Stage IV kit is approximately 20% lighter than the stock brakes and only alter the factory braking bias by about 2%. So far I am very satisfied with the performance of this braking system. It offers neck snapping performance even at 180 mph. Driving on the Nürburgring, I have yet to encounter brake fade even with the standard street pads. Click here for more info.
Brake Pic (1) Brake Pic (2) Brake Pic (3) Brake Pic (4)
After driving the above mentioned ECS brake kit for about 6 months, I took the plunge and installed their Stage 1R rear brake kit. This upgrade swaps the stock rear rotors (modestly sized at 10.1" in diameter) out and replaces them with impressive looking 12.1" rotors. This rear system utilizes a two-piece full floating rotor assembly very similar in design to the front kit. The aluminum hat center section ensures not only improved braking performance, but also reduced unsprung and rotating mass. The stock rear caliper is retained though the use of an offset bracket. A nice side benefit is that the handbrake appears to be about 25% stronger in feel.
Did it help? Absolutely. The car feels more stable under braking (even though the bias is now slightly rearward compared to stock...this tells me that the stock S4 setup may be too front biased) and the brakes are still yet to fade on me. I punished the brakes all day long during a high speed driving event held at the Most Autodrom in the Czech Republic.
At the moment I am running EBC Red-Stuff pads on the front calipers and Hawk Performance HPS compound pads on the rear. I am very satisfied with this setup. Amazingly, the EBC pads put out almost zero dust and rarely squeal when installed with anti-squeal paste. Rotor wear is also a non-issue. The Hawk pads perform well, seem to be wearing well, but dust considerably more than the EBC pads. I may switch to EBC pads in the rear as well. Although the Red-Stuff is not truly a track compound pad, it works well on my car as the Stage IV braking kit has thermal reserve to spare.
The bottom line is this. There are better braking systems available for those truly serious about tracking their cars. For me, my S4 is driven 99% on the road. I do under 10 track events a year and drive VERY fast on the street. I need a braking system that performs very well under street conditions with street compound pads. In this respect, I cannot fault the ECS system at all. Pad selection is improving (multiple pad compounds available from Pagid, EBC, and Hawk). The system is lighter than stock. Braking has improved considerably. It looks great and pad replacement is very simple. I also like the fact that the front calipers bolt directly on the uprights with no brackets required.
 With the increased power output of my Stage III engine modifications, extended hard driving would result in elevated oil temperatures. After seeing upwards of 270 degrees F, I decided it was time to cool things down. I chose the Achtuning Oil Cooler Kit for ease of installation and value. I was able to install this kit without any removal of the front bumper. I chose the recommended 200 degree thermstat. I am very pleased with the performance of this modification. Even under extended WOT operation, oil temperatures will not exceed 250 degrees F. The oil still warms up normally and is about 30-40 degrees cooler than before.
 Controlling the temperature of the intake charge is vital to a turbocharged engine. Too much heat will cause engine knock, timing retardation, and generally less power. The cooler you can keep the intake charge, the better. To keep things in check, I fitted OEM RS4 intercoolers to the car. The pressure drop of these units are significantly less than stock at high flow rates and the intercooler efficiency is greatly increased. The construction is all aluminum (versus plastic endtanks of the OEM S4 intercoolers) ensuring that no leakage occurs at high boost levels. Fitment was fairly straight forward with minimal cutting required. While the intercoolers upgraded, I also had the timing belt and water pump changed out too. Also upgraded was the intake manifold (ported/polished), throttle body (ported/polished), and phenolic intake manifold spacers were fitted.
 More power requires more exhaust flow. The stock downpipes are known for being restrictive due to two catalyst converters in each pipe. Going to a less restrictive downpipe will provide a substantial increase in power. For more info, conact Mike at www.VASTperformance.com
 The STaSIS Track Sports are well known for providing the best compromise between handling performance and ride quality. The Track Sports are Koni adjustable dampers (custom valved/tuned by STaSIS specifically for the S4) with Hyperco springs. Spring rates can be chosen by the customer. I chose a 600 lbs/inch front rate and 700 lbs/inch rear rate. This provides a firm ride which is still very tolerable on the street. The dampers are also the "sport" dampers which are more controlled than the softer "enthusiast" dampers. This suspension setup in conjunction with my Neuspeed 19 mm rear sway bar provides very neutral handling characteristics. The tail can be kicked out in a glorious fashion with full opposite lock oversteer. Fun times!
 With the newfound power and torque, my OEM clutch just wouldn't be up to the task of putting the power to the ground. Unfortunately, I made the mistake of installing a Spec stage 2 Kevlar clutch. After installation, it had been discovered that there had been a number of defective Spec clutches sold including my own. It has been slowly failing since installation and now makes the car nearly impossible to drive. It will be switched out very soon for a unit from www.VASTperformance.com
Defects happen occaisionally. Unfortunately Spec has not been standing behind their products and will not deal with the many customers who are having problems. BUYER BEWARE. I would never recommend this product or company to anyone.
*Update*
I have since upgraded to the VAST Performance Hybrid-modified RS4 clutch with a Kevlar lined friction surface on the disc. This is the clutch I should have bought in the first place. The pedal is not as stiff as the Spec clutch was. In addition, the engagement is much smoother and progressive. This makes the clutch much easier to modulate when launching or simply taking off from a stop. Clamping power is adequate even with my near 500 ft-lbs of torque at the flywheel. I can't imagine another clutch offering the same performance while maintaining such an easy to drive character. For more info, contact Mike or Kurt at VAST Performance.
 This beautiful CNC machined transmission brace holds the transmission securely in place during high torque situations such as launches. It works very well and provides a noticeable improvement in shift quality. Another highly recommended modification. Here is a full sized picture.
 The addition of a high performance exhaust system was another very satisfying modification to my S4. The stock exhaust system is entirely too quiet considering the character of the car. I was very particular with what I expected out of an exhaust. Most of all, I wanted a system which was quiet and subtle at partial throttle (read no droning) but would unleash a more convincing and stirring note when asked. Formerly, the Neuspeed G2 stainless system fit the bill. As the power levels of my car increased, the need for more flow from the exhaust system increased as well. Once the larger turbochargers were fitted, it was obvious that the G2 struggled with the extra exhaust flow. During WOT, the exhaust note made a loud hissing (sometimes called sandblast) noise as the hot gases rushed to escape. My solution was to upgrade to the Autospeed Performance Tru-dual exhaust system. The twin 2.25" mandrel bent stainless pipes provide superior flow compared to a single pipe system. The fitment is quite good. The dual 89 mm tips look massive and are easy to keep clean. The sound is absolutely amazing. It is slightly louder than the G2 system was, but still quite liveable. Droning is minimal to none. I am very satisfied with the purchase of this catback system. More info can be found here.
Here is a short video clip showing the sound and look of the ASP Tru-dual system.
Here is a short soundclip of my previous G2 exhaust for comparison (wav file) The mic was placed directly behind the tailpipe.
 Having sufficiently bright headlights is very important. It is surprisingly easy to "out-drive" the headlights of a high performance car at night. Although the 35 watt, 4,300K system the S4 comes from the factory with is decently performing, there is always room for improvement.
Shown here is a 50 watt 5,400K HID Xenon lighting system (including E-code housings) from SPP.
The European spec (E-code) housings offer superior optics (glass versus plastic) and a much sharper beam pattern when compared to its American DOT code counterpart. The higher color temperature bulbs and higher wattage ballasts offer increased light output (2,800 lumens versus 5,000 lumens. For reference, a 55 watt halogen setup would net approximately 1,500 lumens.) and greater contrast. This picture illustrates how clear and defined the new beam pattern is.
I am very pleased with the performance of this kit. The installation was straight-forward and clean. I feel very comfortable out on the German Autobahns at speeds well over 140 mph during the night time hours. The lights are that good. You will not be able to out drive the coverage.
As bright as these headlights are, they do not cause interference with other drivers. The focused beam pattern is kept very low and is cut off sharply to the left keeping the light out of the eyes of oncoming traffic. Proper aiming is crucial with this setup.
The S4 comes equipped with an auto-leveling headlight system. This keeps the headlights aimed correctly even when the car is tilted above/below level due to loading or dynamic driving conditions. Here is a short video clip which shows the beam pattern and auto-leveling feature in action. Immediately after the headlights fire off, you can see the cutoff raise and lower slightly as the auto-leveling feature performs a self-test.
More pictures of the new headlights can be seen in the S4 Photo section.
Monitoring manifold pressures is vital when dealing with a modified turbocharged engine. If there is any sort of boost related problem with the engine, a boost gauge will quickly alert you of any abnormalities. I chose AWE's vent gauge because their kit is known for matching the interior factory gauges in terms of look and lighting. This kit looks OEM. Also, AWE's included installation kit and instructions are quite comprehensive and easy to follow. I am very satisfied with this modification and would recommend it to anyone with a turbocharged B5 Audi.
 The bypass valve (BPV) is very similar in function to a blow-off valve (BOV) except it allows released charge to recirculate though the intake track. Thank goodness it doesn't make that lame "wooshing" noise too. The stock BPV's are known to be troublesome once boost levels are raised from factory settings. The 710N BPV looks identical to stock...except it has a stronger spring and diaphragm. This is a "precautionary" modification. A faulty BPV will cause boost leakage and can trip fault codes. Two BPV's are required due to the twin turbo plumbing arrangement.
 This small and subtle lip spoiler (OEM M3 part) is a great touch for the rear of a B5 A4/S4. Honestly, this is the only spoiler that I find fits the character of the car. Anything more aggressive looks silly. There are no fit issues between the two cars.
 The 6-speed manual transmission on the S4 is known for being notchy and having long throws. UUC's billet aluminum shortshifter dramatically improved the shifter's feel. This unit can be adjusted to reduce throws by 20%, 30%, or 40%. The backlit shift knob is a cool addition which looks great with the cockpit lighting.
I get numerous emails about this UUC backlit shifter knob. Sadly, this item has not been made for years and is no
longer for sale. Mine included.
 I'm currently running Michelin Pilot Sport tires in the factory 225/45/17 size. This tire appears to be very grippy in both wet and dry conditions. I don't have enough miles on them to assess treadwear yet. They seem to run fairly quiet despite the aggressive directional tread pattern. When I upgrade to 18" wheels this spring, I will likely go with Falken FK-451 tires.
-Custom CNC Machined Pedal Set
2001 Audi S4 biturbo 6-speed manual
Nogaro/Sport/Cold packages
Engine
-K16/K04 turbos (ported, polished, and ceramic coated)
-GIAC IBE II H-box ECU (X, XR, XRR, Stock, Valet)
-Custom homebrew tweaks
-RS4 83 mm MAF housing
-Custom flow matched Bosch Bluetop 36 lb injectors (~490 cc @ 5 bar)
-VAST 5 bar FPR
-TCD MAP clamp
-Piggie MBC in parallel with N75
-N75 K race valve
-RS4 intercoolers
-Achtuning Oil Cooler Kit
-VAST ported polished intake manifold
-VAST phenolic manifold spacers
-VAST ported throttle body
-Samco throttle body boot
-Samco F-hose
-Bosch 710N bypass valves
-Darintake airbox mod with OEM paper air filter
-Piggie downpipes
-ASP Trudual catback exhaust
-VAST Walbro 255lph high pressure fuel pump
Drivetrain
-VAST kevlar hybrid RS4 clutch kit
-VAST short shifter
-VAST snub mount
-ASP drivetrain stabilzer
Suspension/Brakes
-Stasis Tracksport coil over suspension with sport valving
-600 lb/in front and 700 lb/in rear spring rates
-Neuspeed 19 mm rear stabilizer bar
-ECS Stage 4 front brake kit (6 piston/352mm)
-EBC Red Stuff front brake pads
-ECS Stage 1R rear brake kit (307 mm)
-Hawk Performance HPS rear pads
-18x8 RS4 replica wheels
-Goodyear Eagle F1 GS-D3 tires (225/40/18)
Exterior
-Ecode headlight housings
-SPP 50 watt stage 3 HID lighting with 5,400K bulbs
-M5 rear lip spoiler
Interior
-UUC backlit shift knob
-Phatnoise Phatbox MP3 system
-Infinity Basslink subwoofer with remote control
-AWE vent boost gauge
-AutoVation CNC machined S4 logo pedal set
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