With the widebody conversion done, performance tuning was the next prerequisite. Power was achieved through APR's new Stage III. This "bolt-on" kit requires the engine to be removed to access the turbochargers, but did not necessitate upgrading any internals to the motor. Stage III includes a larger intake system, incrementally larger turbochargers (namely K-04s from the RS4), a free flow exhaust system from the turbos back, and some fuel system upgrades. Optional larger intercoolers were added to our car, as well as an aluminum "bi-pipe" from APR, which eliminates the possibility of a torn throttle body boot as a result of the increased boost pressure. All of the changes are managed by APR's EMCS engine software. EMCS stores multiple programs, which the driver can select on the fly. The programs include a valet mode, which limits turbo boost and RPMs, 93 octane mode for normal usage, and 104 octane mode for use at the track. Total sum of all these parts added about 430 hp and 440 ft-lbs. of torque on pump gas. Switching the high flow catalytic converters for "test pipes" (included with the turbo-back exhaust), feeding the car race fuel, and running the EMCS in "race" mode yields about 480 hp.
If you thought a stock or chipped S4 was quick, you should get a ride in a Stage III equipped land-rocket some time - this car is fast. Really fast. There are only a handful of cars that you ride in during your life that mentally slot into your top 10 fastest cars you've ridden in and this is one of them for us. On damp pavement this car will break all 4 tires loose (and we're talking 265mm wide rubber here) and literally claw forward, scrabbling for traction in a display of power only seen in WRC rally cars. Yet, even with all that power on tap, this car can be driven very easily at more sedate speeds, impressing with its buttery power output at a wide range of RPMs. This is impressive stuff.
H&R Special Springs specially developed the suspension on Rob's car for Moto Persona, a Chicago-area tuning shop. They are adjustable height coil-overs, which serve to firm up the car as well as provide an adjustable lower center of gravity, as most sport suspensions do. This suspension differs from regular H&R Coilovers in that they are about 25% stiffer in the rear of the car than the front. This provides balance to the understeering nature of the S4. Correctly valved shocks keep the ride compliant while making it handle like a sports car. APR provided the brake upgrade as well. Four piston front calipers, slotted rotors, and stainless lines were added in front along with slotted rotors and stainless lines in the rear. EBC Greenstuff pads are used for low-dust street braking, and APR race compound pads are switched in at the track.
To improve the interface between driver and car, several other modifications were made. An APR front engine mount solidified the feel of coming on or off throttle, as well as switching gears, and a UUC shortshifter cleaned up the gearbox significantly. Momo pedal covers were installed in an arrangement allowing heel-and-toe downshifting, and a Momo shift knob provides better grip. Recaro "Sport" seats were custom upholstered to match the beautiful S4 interior. These seats, along with Schroth four point harness belts envelop the driver and passenger, and serve to keep occupants firmly in place when necessary. The harness belts can be tucked neatly out of sight when not in use.
Electronic driving aids are often unsightly or overdone, but Rob elected to install two necessities. First, a SmarTire system was installed on the summer and race wheels. It transmits temperature and pressure from each of the wheels on the car to a display unit in the cockpit. Second, a Valentine One radar detector was hardwired in place along with an integrated remote display--a necessity to keep the driver out of trouble in a car with this much potential.
What has been created here is a veritable supercar. It goes, it stops, it handles, it sticks... and on and on. While something on the road will always be faster, or safer, or handle better; be more practical, more subtle, more overt, or just more of anything, this S4 does it all incredibly well - the whole is greater than the sum of its parts. We can't imagine building it any differently and wouldn't change a thing. We'll take two please!
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