S4 Showdown: APR Stage III and AWE RS4

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The venerable and oh-so-tuneable B5 S4. When it was released in 1999, it combined great performance, secure handling, comfort, safety, all weather functionality (with standard quattro all wheel drive) and style into a class-busting sport sedan. From the factory the S4’s biturbo 2.7 liter V6 engine produced a modest 250 horsepower and 258 lb/foot of torque. The word modest is used because the car’s output equates to 93hp per liter, which for a turbo charged engine is not exactly awe inspiring.

Thankfully for Audi lovers, driving the car belies this fact. The turbos spool incredibly fast (almost without percievable lag), and the ease with which this car leaves the line, and overtakes slower cars, is remarkable. The V6 engine is buttery smooth, and very quiet at normal cruising speeds. The S4 could be used to drive Grandma to church in the morning and then put to the test at the autocross later that afternoon.

Luckily for S4 owners who feel that 250hp is just not enough (which turns out to be enough owners to have spawned an entire generation of tuners), the biturbo powerplant is easily enhanced for more power. From simple chip upgrades which can increase the power output to over 300hp (350 lb/ft of torque) to kits consisting of turbocharger upgrades and the other associated parts, the engine is an enthusiasts tuning-dream. From stock 250hp to 350hp and way beyond – the only question is time and money.

For this test we looked specifically at very similar upgrades on separate B5 S4’s owned by friends. Each was kitted with larger turbocharger setups, among other upgrades. Full specs are shown below.

The Contenders:


Jason Peterson’s Nogaro Blue 2000 S4 6 speed.
Hoses: RS4 Complete Kit
Flywheel: SPEC Lightweight Aluminum Dual Mass
Clutch: SPEC Stage III
Intercoolers: APR/RS4 dual side mount
Downpipes: APR w/test pipes
Exhaust: APR 3″ Stainless
Diverter Valves: Stock
Front Brakes” Stock w/ slotted rotors and EBC pads
Rear Brakes: Stock
Shocks: Stasis adjustable w/ remote reservoirs
Springs: Stasis coilovers w/ threaded body
Sway bars: Stock
Boost Gauge: AWE 52mm in dash vent
Wheels: Enkei
Tires: Wanli 225/40 18
Engine Mounts: RS4 Engine Mounts, APR Snub Mount

We’ll skip the tiny bits included in the kit such as bolts, nuts, gaskets, hoses, etc. The most important parts of the kit, obviously, are the two KKK K04 turbocharger units, the RS4 Y pipe, fuel pump, air cleaner box and thye up-rated fuel injectors. It also includes an RS4 Mass Airflow meter and different programming for the Electronic Control Unit (ECU). These parts come off of the European RS4 model, which is essentially an S4 on steroids.

Jason also has other mods on his car which will be detailed later.


Erik Shifflett’s 2001 Santorin Blue S4 6 speed.
Hoses: Samco Complete Kit
Flywheel: AWE Lightweight Aluminum Dual Mass
Clutch: RS4
Intercoolers: AWE/McNeil dual side mount
Downpipes: Milltek w/integrated cats
Exhaust: Milltek 3″ Stainless
Diverter Valves: Bailey
Front Brakes” Brembo 332mm w/ Porterfield street pads
Rear Brakes: Brembo drilled rotors w/ Porterfield street pads
Shocks: Koni Adjustable
Springs: Stock
Sway bars: Neuspeed 19mm rear, removed front bar
Boost Gauge: AWE 60mm in A-Pillar Pod
Wheels: SSR Competition 17/8.5
Tires: Goodyear Eagle F1 245/40 17
Engine Mounts: AWE Drivetrain Stabilizer

AWE’s kit includes, among other things, the highly important pair of RS4 KKK K04 turbochargers, up-rated fuel injectors, a new MAF housing and MAF, the essential ECU software upgrade, and various hoses, clamps, bolts, etc.

Unlike the APR kit, the AWE kit does not upgrade the fuel pump, the air cleaner box, or the Y pipe. AWE also uses non-RS4 spec injectors (Bosch “Green Tops”) and MAF because they feel that the RS4 pieces are maxed out at around 400 hp. The MAF housing and intake hose are enormous compared to the stock pieces.

Driving Impressions:

Compared to a stock S4 (which is not a slouch), a chipped can be appropriately described as fast. The driver benefits from a lot more boost, much more push in the back and much-appreciated top end power. That said, our K04-kitted cars are simply rabid. The first few times at WOT one must give the brain a little extra time to adjust to the thrust. Vision blurs and pulse quickens as the big turbos go to work.

Both of these kits claim to maintain stock-like driveability (a claim we confirm), but when the hammer goes down they come to life in a big way. Each setup does have a distinctively different feel though.

The APR kit seems to make more boost earlier. Running the engine from 2000 rpm in 4th gear seems more effortless with the APR setup than with the AWE kit. When going all out in lower gears the APR kit is positively violent, yanking the driver’s head back against the headrest. The APR rev limiter is also a little more blunt than the AWE programming. During hard driving we found that (in the lower gears anyway) the car built speed so fast that the transmission seemed to bind itself up internally when the rev limiter kicked in. This made it very difficult to shift OUT of the current gear. Granted we were also dealing with a clutch and shifter that we’d never driven before, but it was notable that we did not experience that issue with the AWE-kitted car.

The AWE setup felt like it sacrificed a little low end boost, saving it for later in the rev band. It happily puttered along at 2000 rpm in 6th gear just like the APR car. Standing on the AWE car’s rightmost pedal, however, causes the car to hurl with great urgency down the road. The power does seem to build a little slower (or smoother?) initially, but is no less neck straining. When it hits, it hits incredibly hard. In fact, we felt a new sensation driving Erik’s car. We could actually feel the G forces in our cheeks. Yes, the ones on my face, not in my pants!

Jason’s car has the SPEC Stage III clutch and SPEC flywheel, which we’d never driven before. Strangely, the very first time getting it moving we had no problem. Each subsequent pull away from a stop, however, was more clumsy for some reason. This probably had a lot to do with our brain still being back at the last stop sign and still adjusting to the car’s extra power. Perhaps it was all Erik’s fault since he was goading us with a slightly evil grin, saying “floor it, floor it” the whole time.

Erik’s car employs the RS4 clutch and AWE flywheel which elicited what was essentially a stock feeling, yet took every ounce of work we threw at it. In all there was zero hint of complaints from either clutch. We liked the feel of Erik’s clutch off the line, but the clutch/light flywheel combined with the pedal covers on Jason’s car made honest to goodness heal-toe downshifts a snap. A shortshifter may have made it perfect.

Handling wise the cars were night and day. Suffice it to say, we highly recommend the the Stasis Motorsports kit. It was far more smooth than the stock springs/Koni setup in Erik’s car, it took rough roads better, the car didn’t squat (or dive) and the handling balance was neutral. During the test we were able to upset Erik’s car in a somewhat rough left hand bend under full power. The intent was oversteer, but what we got was a chattering inside front tire. The car is crying out for more suspension. It was by no means loose or undriveable, but as many B5 S4 owners know the powerplant’s performance can very quickly expose the deficiency of the stock suspension.

Brake wise it was no contest towards Erik’s car with his Brembo calipers on 332 drilled rotors. Part of going fast is stopping fast, and Erik’s car does that very well (and over and over again) without hesitation. Jason’s car has nearly stock brakes, which while strong are prone to fade and are weak point in his car’s setup.

Now, on to the really fun part which actually took place indoors…

The Dyno:

KTR Performance, in Ayer Massachussets was gracious enough to invite us to use their amazing facility for our testing. KTR is the real deal, the shop was wall to wall eye candy, from Porsches to Ferraris, Nobles, Subaru STIs in various state of tune.


We spent a good bit of time drooling on the cars. See the gallery for more pics. Now on to the dyno.

KTR uses a Dyno Dynamics chassis dynamometer. Compared to many other types of chassis dynamometers, these are said to read ‘low’. So, the numbers we see here will not look at all like the ones on the other dynamometers. What we did to show the general baseline was bring along Rob (‘Bahn Burner) and his stock 2001.5 S4 6 speed.

While I was busy pacing like an expectant father waiting for Erik and Jason to arrive at KTR with their friends Mark and Mark, who run East Coast European, up in Greenland NH (They were hustling to get Jason’s new APR RS4 intercoolers on his car that very morning), Franz Diebold, General Manager and tuning wizard (not to mention, really cool guy!) strapped Rob’s silver S4 onto the dyno, and started calibrating it for the car. Franz explained that the Dyno Dynamics machine is an inertial style dynamometer, so it needs to know a bit about the car that’s running on it. Also, Franz did give us an estimated crankshaft power figure, but I’m sticking with the power at the wheels, because that way there is no interpretation required.

Stock 2001.5 S4 6 speed, stock ECU:

burner_dyno stock_small

This is stock, at the wheels. Since we were still waiting for Erik and Jason, Franz put Rob’s APR chipped ECU into the car, and did some more pulls. The results were pleasing to me, because, even though the car seemed to be making very low power (Franz said what we saw was actually quite good for a stock S4), the increase from stock to the chip was exactly what we’d expect it to be. Again, that was at the wheels.


2000.5 S4 6 speed, APR Stage 3 RS4 Kit (running on 112 octane race gas, on the APR race gas profile):

Here is Jason’s car, strapped to the dyno, screaming it’s lungs out.


Jason and Erik were both running the same 112 octane racing gas, as they both wanted to see what the cars would do on that rating of fuel. We ran Jason’s car in the race profile, and in the pump profile, which showed a significant difference, even though it was still running the 112 fuel. The below dyno chart is on the race profile, at the wheels.


2001.5 S4 6 speed, AWE Stage 3 RS4 Kit (running on 112 octane race gas, on the AWEpump gas profile):

Last but not least, Erik’s car was strapped to the dyno. The car was set in pump gas mode for the first pulls, even though it had 112 in the tank. This car made a wholly different sound than Jason’s and Rob’s cars. It was much throatier, we all noticed that right away.


Strangely, Erik’s car made more power on the pump profile than on the race profile. Franz saw that the car made more boost in the pump profile (he had hooked into the vac lines so the dyno would see manifold pressure)


In the end, we were left wondering why the APR car made so much less than we thought it should. Was it a bad O2 sensor? The exhaust gas analyzer read that the car was running very lean. That may have had something to do with the lack of power. It didn’t seem to be pulling timing, and it was running basically the same boost levels as the AWE car. Perhaps we’ll never know. Maybe one day we’ll have a chance for a rematch.



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