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Audi S4 Tuning Guide

When Audi released the S4 in late '99, everybody went nuts. At that time, no other V6 in the States had a twin-turbo engine this side of the $120k Porsche Turbo, never mind all-wheel drive.
The 2.7 liter started with 250hp and 250 lb/ft at the flywheel, good for a 14sec quarter at nearly 100mph. With four doors and room for five, this ultimate hauler continued its reign until '02.
In this article, we're using 200hp at the wheels (whp) as our baseline, indicating 20% drivetrain losses. But gains vary from car to car. To calculate engine hp, divide whp by 0.8.
Also note, installation costs aren't included but should be considered since a turbo upgrade can take several hours once the engine is removed.
Furthermore, importers of European products like RS4 turbo kits are at the mercy of fluctuating exchange rates, so prices can vary.
$0-1000
As always, a decent intake system gives the best bang for your buck.
AWE Tuning's S-flow intake uses an ITG filter that sits in the factory airbox, intended for light mods with stock turbos. For $190, you can expect an 8whp gain with a 205whp peak.
ABD Racing has the Quick Flow intake for $270, which gives 5-6whp. ABD also has the Big Bore intake with 3.5" ceramic-coated tubing and silicone couplers for $165.
APR has a $599 software upgrade with an optional switch to toggle between stock, pump gas, race fuel, and valet modes. You should expect over 245whp on 91-octane with 292 lb/ft, or 255whp with 306 lb/ft on 93 at 1bar (14.7psi) boost. APR also has an O-ring sealed aluminum BiPipe for $349, replacing the boost-leaking throttle body boot.
Neuspeed's $450 software, added to a K&N drop, should net approximately 50whp CARB-legal at 1-1.2bar.
Autospeed Performance (ASP) has stage 1 software, providing performance and stock codes, as well as valet and kill programs, all for $549. Expect 50whp and 90 lb/ft on 93-octane. There's also a shift light and launch control option. With ASP's $199 1.4 lb 6061 aluminum crank pulley (6 lb stock), expect 8-10whp. Throw in ASP's phenolic intake insulation spacer and you'll be saved from heat soak.
The $130 spacers reportedly reduce intake temps by 10.
Those wanting larger turbos should consider ASP's 85 and 90mm MAF housings for $330 and $389 respectively, allowing for custom tuning.
Other ASP components in this price range also reduce drivetrain losses. One is a $249 billet transmission stabilizer bar, which ties the tranny to the chassis through a rubber bushing. There's also $395 billet engine mounts with two stages of urethane bushings, making shifting easier so more power can be transferred to the wheels.
AWE sells its billet Drive Train Stabilizer (DTS) for $349. Since many S4s rack up the miles, AWE sells factory RS4 engine mounts for $130 each - something to think about when upgrading to K04 turbos.
Since the two factory diverter valves are weak links, Forge Motorsport sells $150 billet replacements that improve throttle response and maintain reliable boost.
AWE also sells $160 Bailey Motorsport diverter valves in either polished or black. While replacing a faulty DV, the Bailey valve revealed the old unit lost 8% horsepower during AWE's dyno tests. They also sell Samco hose kits for $445, replacing all boost hoses on high mileage engines.
Dahlback Racing has a $599 chip upgrade putting out 250whp and 315 lb/ft. With a decent cat-back, these figures can be increased to 260whp and 320 lb/ft, respectively.
ECS Tuning sells a $270 aluminum pulley kit, designed to add a few hp by reducing rotational mass instead of underdriving the accessories. This includes the crank, power steering and alternator pulleys, each weighing 683, 307 and 123 grams, respectively.
Evolution Motorsports (evoms) sell a CAD/CAM designed venturi-type intake that acts as a vacuum. The patented $299 V-Flo reportedly gives 10whp. Also available is a $289 cold-air intake system (CAI) with a thermal-coated aluminum heatshield.
GIAC offers software for stock turbos at $595, netting 50-60whp at peak, with 60-90whp in conjunction with a good exhaust. The $795 stage 3 "minus" software for K04 turbos uses a 5bar Bosch fuel pressure regulator (FPR) and stock injectors. AWE, evoms and Torque Factory are GIAC distributors.
Several companies have cat-back exhausts which fit this category. Borla has a $867 stainless steel unit with center resonator. APR's $999 stainless system starts with twin 2.25" tubing, merging into a single 3" pipe - a center resonator is $100 extra for the quieter version. ASP's $1000 system includes two resonators with 2.25" stainless tubing and either 3 or 3.5" tips.
Neuspeed has the most economical set at $770. Its dual resonators and stainless construction meet state noise resistrictions.
Joe Hoppen Motorsport sells $595 MTM software for different setups. For the stock S4, it produces 245whp with 285 lb/ft. Cars with cat-back exhausts and FPR can net 275whp and 308 lb/ft. For those with RS4 turbos and a full exhaust, the MTM software boosts to 20psi and produces 300whp. Its final software retails for $650. Geared toward vehicles with full RS4 upgrades, it's said to be good for 335whp.
Revo Technik sells $599 software good for 250whp and 292 lb/ft peak torque on a stock engine. Revo also offers three stages of Serial Port Switches from $199-$349, for different octane, boost control and anti-theft security.
Stasis Engineering offers a Torsen center differential for $550. The stock diff provides 66% of its power to the rear (2:1), but the Torsen provides 80% (4:1), the same ratio as the RS4.
Techtonics Tuning is the only firm in this category to offer downpipes at $999. They start at 3", taper to 2.5" and include 400-cell cats. Reportedly, they fit a stock exhaust or TT's own cat-back system.
Avalon Motorsports offers South Bend clutch kits for modified S4s. The stage 3 OFE retails at $749 and uses an organic/kevlar compound on one side and a Feramic, iron-based compound on the other for heat resistance and higher clamping loads. They should withstand 420 lb/ft to the wheels. Its $825 stage 4 is fully Feramic, and resists 480 lb/ft and higher. Both fit the factory flywheel or a lightweight Fidanza unit.
If oil temp rises, Matrix Engineering has a 25-row Mocal oil cooler kit and thermostatic adapter for $497. It fits either stock, RS4 or AWE side-mount intercoolers, plus front-mount intercoolers (FMIC) with custom brackets. Customers saw 30-40 drop in oil temps on track.
$1000-2000
Matrix offers S4 cams, which retail at $1099 and work with factory valve springs and retainers. Two different cam profiles are available, but a $900 core charge is extra.
Avalon sells an RS4 intercooler upgrade, including the shrouds and silicone hoses for $1125. The optional bracketry is an extra $100.
Techtonics has a dual 2.5" exhaust system made from 304 stainless with Borla mufflers and chrome tips for $1195. It offers two different versions for stock as well as its own downpipes.
ASP sells CAD-designed 3" downpipes for $1500, which includes CARB- and DOT-legal cats, CNC mild-steel turbo flanges and 304 SS tubing. With a stock cat-back and ECU, you're looking at 24whp gains.
APR's RS4 intercooler kit includes custom aluminum end tanks, silicone hoses, two BiPipe hoses, mounting hardware and a horn relocation bracket for $1498.
Cars with K04 turbos or bigger, ASP's $1850 tubular exhaust manifolds include 304 stainless construction, Swain Tech coating and are port-matched. They reduce exhaust gas temps and improve turbo spooling. Expect 25whp gains at high rpm thanks to increased flow.
AWE is proud of its $1396 dual side-mount intercooler (SMIC) upgrade. The cores are 65% larger than stock and 57% bigger than RS4. At over 5000rpm, AWE has reportedly seen a 10 drop on intake temps over RS4 units, and 50 over the heat-soaked stock parts. At 20psi boost, the units saw a 1psi pressure drop versus up to 2.5psi for the stock cores. Testing was done on AWE's dyno using a K04-equipped S4, which jumped from 324whp to 344whp.
Intercooler specialists Evolution Racewerks have both a dual SMIC and FMIC upgrade. Both are a factory fit, with no cutting required. The 15-row cores on their side-mounts feature bar and plate design, and flow 360 cubic inches apiece. The kit retails for $1395 and is available through Eurocode Tuning or Wicked Motorsports. The front-mount is expected to sell at around $1995 but prices have yet to be finalized.
Italian exhaust manufacturer Supersprint sells a $1620 cat-back made from 304 stainless with a center resonator.
For $1700 Neuspeed has its titanium Race Series cat-back exhaust that weighs just 9 lb.It's meant for racing but there's a street-legal baffle for street use.
$2000-3000
Stasis has a $2095 limited-slip rear diff with 40% or 60% lock up, so you can put more power to the ground mid-turn or during straight-line acceleration.
ASP's large FMIC measures 28.5x6x3". The $2200 kit features cast end tanks, an easily programmable 16" SPAL fan, billet cooling fitting, custom silicone hoses, black powdercoated piping, oil and power steering coolers, plus braided lines.
Combine ASP's $1550 3" downpipes with its $1000 2.25" stainless steel, mandrel-bent cat-back exhaust and you'll end up with up to 230whp on a stock S4, minus ECU upgrades. Throw in ASP software and you have 295whp.
Avalon offers an RSK04 turbo upgrade with installation hardware, including silicone hoses and a Bosch FPR for $2575. Software is available on request at additional cost. Avalon also offers RS4 engine conversions, but prices vary with exchange rates.
The AWE tubular exhaust manifolds cost $2995. The header flanges are fly-cut and come Swain Tech coated. They give a peak 10whp gain at high rpm and over 20 lb/ft down low over stock. You can earn a $200 discount when its ordered with AWE's K04 upgrade.
Exhaust specialist GHL Motorsports takes pride in Rath-Gibson aircraft quality 304 stainless steel, which is about three times more expensive than imported 304. It's cat-back system retails at $930 and the downpipes are $1435. The downpipes use 400-cell ceramic high-flow cats, but GHL can include two extra test pipes to replace the cats if desired.
A Milltek cat-back and downpipe combo runs $2998 purchased through Stratmosphere. The German-made, platinum-coated, 200-cell cats give 85% open cross-section.
If you want to build your S4 heads, Matrix Engineering offers Supertech intake and exhaust valves, stiffer springs, titanium retainers, locaters, and solid lifters for $2457.
$3000-$4000
APR stage 2+ includes its $599 stage 1 software, as well as its stainless downpipes and cat-back, bringing the total to $3097. The downpipes remove the factory pre-cats off the turbos. They include two pipes off each turbo, a set of pipes with cats and test pipes without cats. The cat-back starts with twin 2.25" piping and merges to a single 3" muffler. You can expect around 270whp with this setup on stock intercoolers.
For the S4 that just blew its turbos, factory K04s is the way to go for both price and power. Any GIAC dealer can sell you the stage 3 "minus" software, aimed at people who can't afford a full stage 3 kit yet. All you need is a Bosch 5bar FPR and the turbos, which you can get from companies like AWE, Torque Factory and Evolution Motorsports. It works with the stock intake, injectors and exhaust. The setup will run about $3800 and will work on Tiptronic cars. Expect around 290whp.
$4000-5000
If you've got the coin and want Oettinger products, CEC imports the full, hand-built, stainless steel exhaust system. The cat-back retails for $2500. The downpipes go for $2000, plus an extra $3000 if you require the 100-cell motorsport cats.
Dahlback Racing reports it hits over 295whp from the stock K03s when using its 3" downpipes with 100-cell cats, specific software and RS4 intercoolers. The kit retails for $3495 and includes all hardware, but you'll need a cat-back as well. Keep in mind you'll also probably need a new clutch, which Dahlback has for $2100, including disc, pressure plate and single steel flywheel.
Stratmosphere's stage 3 system retails for $4300 and includes Milltek downpipes, 3" cat-back exhaust, Hyperboost diverter valves, 5bar FPR and O.CT stage 3 software. Expected power is 265whp with 320 lb/ft as early as 2300rpm.
$5000-6000
ASP offers a stage 3 K04 Motorsport turbo kit. It includes: K04 turbos, fueling kit with 60 lb/hr injectors and phenolic fuel rail spacers, 85mm MAF housing, coolant temp sensor, in-house software, plus hardware and gaskets for $5200. ASP recommends its downpipes, RS4 clutch and intercooler with this kit.
$6000-$8000
Give AWE $5250 and you get a RSK04 turbo upgrade, turbo inlet piping and installation hardware to the downpipes. This kit also includes AWE's optional fuel system with balanced Bosch injectors, spark plugs, GIAC software, AWE MAF housing with adapter, silicone hoses and all hardware. For '00-02 models, the Bosch MAF must be converted to a Hitachi unit, adding $300. AWE reports it doesn't use OE RS4 injectors because the spray pattern doesn't suit US-spec S4s. AWE also claims its downpipe ($1595) and cat-back system ($995) are needed to run this kit. The firm further recommends its intercooler upgrade ($1396), Samco hoses ($400), DTS bar ($349), RS4 engine mounts ($260) and RS4 clutch kit ($495). Tiptronic S4s need a level 10 transmission upgrade to run this kit.
Dahlback's stage 3 K04 upgrade includes turbos, fuel pump and injectors, RS4 intercoolers and downpipes. It costs $5195, but a cat-back system is also required. In testing, it's shown 370whp and 365 lb/ft on pump fuel, with 430whp and 440 lb/ft on 100-octane.
$8000-10000
Stratmosphere's stage 4 upgrade uses K04 turbos with special turbine wheels to provide K03-style spooling, but K04 top-end. Everything's included for $9400, making 300whp with 325 lb/ft from 2300-4200rpm. The kit includes Milltek downpipes and 3" cat-back, Hyperboost DVs, throttle body boot, special plugs and 5bar FPR.
$10000-12000
The $7249 APR stage 3 kit includes two RSK04 turbos, plus the MAF, airbox, Y-pipe, turbo inlet piping, fuel pump and injectors from the RS4. It falls into this price bracket because downpipes and a cat-back are needed, adding $2498 and nets you 340whp. You should also add APR's intercooler upgrade to be around 360whp with 360 lb/ft for a grand parts total of $11245. A clutch is highly recommended as well.
If you took ASP's $5200 stage 3 K04 Motorsport turbo kit and added the recommended downpipes ($1550), cat-back exhaust ($1000), intercooler ($2200) and RS4 clutch ($800), you'd reach $10750, with a reported 400whp and 415 lb/ft on 93-octane.
If you're in need of a new engine, it's a good time to consider bumping up to 3.0 liter. ASP offers its 3.0 short block, bored-out and fitted with a forged ASP crank, rods and 8.5:1 pistons. The built short block costs $6500, but requires 2.8 liter heads with an upgraded valve train to bump the rev limiter to 8500rpm, bringing the total to $10000. ASP reports this upgrade is good for anybody after 900whp!If you dream of converting your S4 to RS4 performance using factory components, ECS Tuning has what you need. Starting with the engine, it's got the RS4 intake cams ($594), intake manifold ($420), fuel rail, pump and injectors ($1969), timing covers ($90 pair), head gaskets ($110), intake manifold and throttle body gaskets ($18), airbox and air mass sensor ($820), intake tube ($60), pressure pipes ($840), throttle body ($820), Y-pipe ($650), complete RSK04 turbo kit with inlet pipes ($2750) and intercooler ($750). If you include the RS4 engine cover ($740) and oil cooler ($1099), your total is $11730. The "380hp" RS4 puts out over 300whp stock.
$$$ Rich and Shameless
If your S4 is bone stock, you can double your power with AWE while maintaining good spooling. You need their RSK04 turbo kit with stainless and coated tubular manifolds and fueling system, plus the side-mount intercooler kit ($1396), downpipes ($1595) and cat-back ($995), bringing the total to $9236 ($10145 for '00 models converted to Hitachi MAF). Additionally, you'll need the RS4 clutch ($495) and a turbo-back system ($2590) to fully benefit, for a grand total of $12321. AWE has seen 380whp and 370 lb/ft on 93-octane, and 416whp and 428 lb/ft using 103. Thanks to the exhaust manifolds and GIAC tuning, 20psi is reached by 3000rpm.
ASP's cream of the crop is its $15500 GT28RS turbo kit. Along with the Garrett turbos with modified housings for better fitting, you get in-house software, ASP tubular and coated headers, downpipes with high-flow cats, 38mm Tial wastegates, split wastegate tubing, stainless lines, hoses, gaskets, 90mm MAF housing, 60 lb/hr injectors, 4bar FPR, Bosch Motorsport fuel pump, platinum spark plugs, phenolic spacers and ASP's FMIC kit. You'll also need a clutch kit ($800), which is sprung for a factory feel. Additionally, you'll need a cat-back ($1000) to fit ASP's downpipes, bringing your new total to $17300. The result is a whopping 560whp with 590 lb/ft on 93 octane, and 635whp and 611 lb/ft on C16 race fuel.
If you want a really fat torque curve, Stratmosphere's highest power upgrade is its $17959 stage 6. It includes quick-spool K04 turbos with hardware, low compression gaskets, MAF assembly, RS4 fuel pump with O.CT injectors, 5bar FPR, plugs, Milltek turbo-back, O.CT software, RS4 intercooler and oil cooler, Stratmosphere stage 2 clutch and flywheel, silicone induction kit and two diverter valves. The kit puts out 345 lb/ft of torque from 2500-4500rpm, only dropping to 300 lb/ft by 5700rpm. Peak power is 345whp.
Known for its fast cars, Dahlback's daily-driven S4 makes 520whp and 464 lb/ft on pump fuel using company pistons, rods and heads port-match to the RS4 intake manifold. The K16/24 hybrid turbos flow through RS4 intercoolers and throttle body. It also uses diverter valves, injectors, Bosch fuel pump and downpipes. Dahlback will install this engine for $35000 plus a cat-back exhaust.
Although primarily AWE dealers, Wicked Motorsports offers its "stupid-power" package. It includes a built motor to reach 800whp on race fuel with a custom GT2871 turbo kit, Innovate Systems headers and downpipes, built 2.8 liter
O-ringed motor using JE Pistons, Cunningham rods, nitrated crank, main and head studs, a worked head with oversized valves and custom cams, RS4 gaskets, Aeromotive fuel pump, fuel rail and 65 lb/hr injectors, RS4 intake manifold, Evolution Racewerks 4" side-mount intercoolers and Clutch Masters clutch and flywheel. The system is controlled by 034 Motorsports engine management. This setup will run over $26000, but don't forget 45-plus hours of labor.

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