|May 30, 2006
S4 Showdown: APR Stage III and AWE RS4
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.
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.
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.
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...