"The big advantage this time around," explains Chris Berube, lead development engineer for the Cadillac CTS-V, the performance version of the Cadillac sedan "was that the V model was planned from the start, and the all of our requirements were baked into the base car." Consequently, the program was faster and the engineers were able to add content. For example, the 2009 CTS-V has an optionally available automatic transmission and its predecessor did not. "There was no way to retro-fit a high-capacity automatic into the old car," says Berube, "without significantly modifying the floorpan." That problem was solved with the addition of an all-wheel-drive variant in the second-generation model so there is more than enough room for either a Hydra-Matic 6L90 automatic or Tremec TR6060 manual transmission. "We then looked at the planned powertrain package and the expected loads through the body, and integrated that into the basic all-wheel-drive structure," says Berube.
As is becoming commonplace at GM, the CTS-V was built as an analytical model long before the first physical prototype was completed. This not only allowed the performance integration engineers to run through multiple iterations before any parts were built, it helped them meet their tight, 24-month timeframe. "It's definitely been a case of 'Fast Car, Fast Program' for the CTS-V," says Berube, who implies that all derivatives of mainstream models are held to the same schedule at GM. As the volume version moves along the development timeline, small teams are created to develop each variant at set points in the process. Communication between the main and specialty groups is coordinated on a weekly basis along a two-way path, with the mainstream engineering group acting like a tree trunk and the smaller development groups as branches.
The LSA engine, a supercharged 6.2-liter V8, was developed alongside the LS9 used in the Corvette ZR1. A smaller, 1.9-liter version of Eaton's sixth-generation supercharger is used; it provides more than 400 lb-ft of torque from 1,200 rpm, and its four-lobe rotor design helps cut noise 10 dB compared to a three-lobe rotor. The LSA has integral piston oil squirters to keep crown temperatures in check; an intercooler mounted atop the engine under an acoustic engine cover; a single-unit intercooler and a 9.0:1 compression ratio. It is built alongside GM's high-volume small block V8s in Silao, Mexico. It produces 556 hp @ 6,100 rpm and 551 lb-ft @ 3,800 rpm.
As mentioned earlier, the CTS-V offers a pair of transmissions. The Tremec TR6060 is based on the T56 six-speed used in the previous CTS-V, but replaces the single-plate clutch with a dual-plate design that achieves higher clamping power, a lower shift effort, and lower inertia. The old car's dual-mass flywheel is retained. In addition, the shift pattern's throw has been shortened, and the space between the accelerator and brake pedals has been reduces to 60 mm to encourage heel-and-toe downshifts under hard use. The Hydra-Matic 6L90 also has six forward speeds, and-according to Berube-"is the highest torque capacity automatic in GM's arsenal short of an Allison transmission." It uses a twin-plate torque converter clutch, the first used with GM's 300-mm torque converter. This gives the unit greater torque capacity and clamping force. Drivers can select their own gear via the gear lever or steering wheel paddles, and a performance shift algorithm comes into play under sustained high-performance driving to hold each gear longer, make each shift more aggressive, and prevent upshifts upon entry into corners.
Though owners of the previous generation CTS-V complained about that car's tendency to "hop" its independent rear suspension under hard acceleration, Berube's team took the opportunity to upgrade the entire driveline. The upsized propshaft is a two-piece design with a center bearing and a constant velocity joint on each end. It feeds into a cast-iron differential case and out through stronger rear halfshafts. To eliminate hop, the strengthened shafts are asymmetrical-a hollow 55-mm unit on the driver's side and a solid 35-mm shaft on the passenger's side-to de-couple the wind-up and release forces. This change worked so well, Berube claims, that, "the ZR1 guys borrowed the idea from us."
Suspension and Brakes
The independent front and rear suspensions feature short- and long-arms isolated via elastomeric bushings. The CTS's stock 29-mm hollow front anti-roll bar is retained, as is the stamped steel rear subframe. The rear suspension is fitted with a solid 24-mm anti-roll bar, and the spring rates have been raised to 65-N/mm in front and 90-N/mm in back. The CTS-V is fitted with magneto-rheological dampers that use information about lateral acceleration, wheel speeds, and steering angle to adjust the damping forces in real time. This gives a broader range of damping authority without sacrificing ride for handling, and also allows the driver to choose from one of two modes: Tour and Sport.
For a 4,200-lb. (4,300-lb with the automatic) sedan capable of traveling from 0-60 mph in 3.9 seconds and topping out at 191 mph (175 mph with the automatic), braking was a high priority. Italy's Brembo supplies 380 mm x 32 mm vented front discs clamped by six-piston calipers, and 373-mm x 28-mm vented rear discs with four-piston units. The front discs are co-cast, that is they join a cast iron disc and aluminum hat section in a single unit. This not only pulls more heat away from the front wheel bearings faster, it saves more than two pounds per rotor.