But one weak link in the driveline is the floppy mounting of the transmission, which can result in some unwanted movement and vibration. To cure this, AWE markets a "drivetrain stabilizer" that is called just that: the DTS. It works by solidly tying the transmission to the motor mounts, using some otherwise unused threaded bosses on the transmission case. (Todd speculated these are used to install the trans while the car is being assembled.) This prevents unwanted movement in the drivetrain. The DTS is a lightweight unit made entirely of aluminum, bolts in easily in about 15 minutes and is available for most recent VAG cars with a manual transmission. The idea is to keep the drivetrain from rocking around, which largely is the result of soft motor mounts. There are no side effects resulting from the extra stiffness. Todd reports the installation doesn't make the car ride any harsher than stock, nor does it cause any extra vibrations. This results in better, crisper shifts and improved throttle response as the engine and driveline doesn't jump as much under hard acceleration and shifting. Todd said that approximately 900 of the bars have been sold since its introduction.
The carbon-hooded car has an RS4 clutch with AWE's lightweight flywheel. "The RS4 clutch is supposed to have the same friction material and clamping force, but we find that they look completely different; they are supposed to be the same part number. The pressure plate can withstand 500 more pounds of clamping force; you can throw anything at those and they'll handle it. The Silver Bullet has a dual, fiber-type clutch, which AWE developed in concert with ClutchNet." The idea there was to help the car survive very hard launches. AWE finds the downside of being able to withstand these launches is shorter clutch life than normal. The stock flywheel weighs in at a portly 26 lb, while the AWE lightweight unit in all three cars is a downright petite 12 lb, which results in much quicker shifting. Tanoga short-shift kits are also installed in each of the cars for shorter throws and faster shifts.
In addition to offering Borla exhausts for the S4 and other Audis, AWE has its own line of cat-back exhausts and downpipes for increased performance. Where the AWE exhausts differ from a number of the designs coming over from Europe is due to the stricter U.S. OBD-II requirements. In some of the European units, 100-cells-per-sq-in. catalysts were used instead of the factory's 400-cells-per-sq-in. cats. AWE has found, at best, the 100-cell units possess a 2- to 3-hp advantage over the factory cats.
And there is a disadvantage to the 100-cell units, as AWE found. "The downside is these cats cannot maintain the catalytic action over the life of the cat. So you end up with a 'check engine' light after about 1,000 hours of operation, because enough of the precious metals have been used up to let the levels the second oxygen sensor sees go above the OBD-II limits. They don't work; they don't meet the standards, so we use a 400-cell unit," said Todd.
The Twin 2 exhaust AWE sells for the S4 is a true dual unit, with two pipes going from the catalytic converter to the back of the car. The factory Audi exhaust merges right after the main cat. Todd pointed out the engineering details: "There's more room in the A6, so it has twin pipes. In the S4, it's like stuffing a 10-lb turkey into a 5-lb bag, but we came up with a design that works. Kenny came up with a system that would work without flattening any tubes. It maintains a constant diameter of 2.25 in. from the catalyst back to the tailpipes. So there's no turbulence issue at the merge, and you retain velocity. You have about 11% more cross-section area than a single 3-in. pipe. The pipes are all T304 stainless steel with beautifully designed tips. It is quieter than most, which AWE finds most S4 customers want.