We wrote in detail about the
CTS-V's powerplant back in January, but this is the first opportunity we've had to experience the beast up close. With the supercharged 6.2L LSA V8 now officially outputting 556 hp and 551lb-ft of torque, perhaps the single biggest problem is putting it to use. Turning all that power into kinetic energy can easily cause all manner of mayhem at the drive wheels (rear, of course). Since roads are rarely as uniform as we would like, and the vertical forces acting on the tires are almost never equal, one drive wheel usually looses traction before the other. Once that happens, the drive torque gets sent over to the other wheel via the traction control systems and limited slip differentials.
When the engine produces a lot of torque, the half-shafts twist like a spring and then release when the tire looses traction. If the half-shafts are identical in size, the release on one side can cause the other side to wind up and then reverse the process. Exciting the system in this way ultimately causes the wheels to start bouncing around in a phenomenon known as axle hop. When the wheels start hopping, the car doesn't accelerate and, if you're trying to accelerate out of a corner, you can easily get totally out of control.
Most manufacturers try all kinds of fancy suspension geometries and control schemes to get axle hop under control. The GM suspension engineers decided to go back and look at the root cause of the problem and discovered that it was triggered by the half-shafts alternately winding up and releasing. After analyzing the problem, they discovered that by changing the effective spring rate of the axle shafts they could virtually eliminate axle hop by ensuring the oscillation frequency of each side was different, thus eliminating the excitation that was occurring.
They did this by making the left half-shaft (above, left) almost twice the diameter of the one on the right (above, right). The result is that even with all that torque, the CTS-V has some of the cleanest, smoothest launches with no skittering or bouncing around. The system works so well that GM has applied for a patent on the design and the Corvette ZR1 uses the same setup.
The other main mechanical difference in the suspension is the second generation Magne-Ride system. The basic principal remains the same, but the implementation has been refined. The hydraulic fluid within the dampers is impregnated with iron particles. When electro-magnets in the dampers are energized, the viscosity of the fluid is continuously varied to get just the right damping rate. For the new version, the shape of the pistons has been revised allowing for a greater dynamic of control. The controls engineers have also played an important part in upgrading Magne-Ride. The software now features more feed-forward control that looks at the inertial sensors (yaw-rate, lateral acceleration, longitudinal acceleration) and the driver inputs (steering angle, throttle and brake) and anticipates the direction that the car is going to adjust the dampers preemptively. If the driver turns the wheel to the right while hitting the brakes, the left front damper will tighten up before the weight transfer even occurs.
All of this stuff works amazingly well on the track. On the north-south straightaway at Milford, Lead Engineer for Performance Integration Chris Berube gave me a ride in the silver car that Heinricy used to set the 'Ring record. Regardless of whether Chris simply moved his right foot from the brake to the gas or used both feet to induce a smoky burnout, the back end of the Cadillac stayed planted and pointed in the right direction. There was no sign of any bouncing either from inside the car or watching from outside. The only feeling was pure, unabated acceleration. The record car was equipped with the 6L90 automatic transmission and even this high-powered monster had incredibly fast and smooth shifts. In fact, the shifts were so smooth and perfectly matched to the engine speed that the car felt more like an electric drive than an internal combustion beast.