The V6 delivers 302 horsepower at 6300 rpm and 272 pound-feet of torque at 5200 rpm.   It delivers good fuel efficiency, while its direct injection technology enables a 25-percent reduction in cold-start hydrocarbon emissions.   With direct injection, fuel is sprayed directly into the cylinder, rather than into the intake port.   As the fuel vaporizes in the cylinder, the air and fuel mixture is cooled.   This enables the use of a higher, 11.3:1 compression ratio for better thermodynamic efficiency.   The 3.6-liter V6 also features an isolated fuel-injector system, which helps reduce engine noise.  

The six-speed automatic that comes on all models features a generous 13.88:1 maximum overall first-gear ratio for rapid launching off the line (13.11:1 with AWD), while also providing two overdrive ratios that decrease engine rpm and reduce noise levels while cruising at highway speeds.  

The V8 generates 320 horsepower at 6400 rpm, and 315 pound-feet of torque at 4400 rpm.   Both the 3.6-liter V6 and 4.6-liter V8 use electronic throttle control, to match the engine's performance to a variety of driver demands, from sedate highway cruising to rambunctious back-road motoring.  

We especially enjoy the STS V8 with the optional performance handling package.   Nudge the shift lever over to the right, into the manu-matic gate, and the selected gear will hold all the way up to the engine's redline, and this car can be taken to extremes heretofore beyond the reach of sedans wearing the Cadillac wreath and crest.   The suspension engineers have demonstrated they understand the difference between too stiff and responsively firm.   Thankfully, all the sound filtering and deadening doesn't keep the V8's throaty exhaust note out of the cabin.  

The all-wheel-drive system is a hard package to top, complemented by Magnetic Ride Control and the latest generation StabiliTrak, though this adds some weight.   Body lean in even the tightest switchbacks is minimal and mild dips are well controlled.   Biasing 60 percent of the power to the rear wheels gives the all-wheel-drive STS the sporty dynamics of rear-wheel drive while sending enough power to the front wheels to help in bad weather.   It's a good setup.  

The electronic steering is a delight, its only shortcoming a slight softness on-center.   The STS tracks well into and through corners, especially with the 18-inch, low-profile tires.  

Active steering, available exclusively on V8 models with AWD, is integrated into the StabiliTrak stability control electronics.   In addition to controlling brakes and reducing engine power, StabiliTrak with active steering can turn the front wheels to reduce skidding when rear wheels lose traction.   The system includes a new steering motor assembly combined with computer-driven electronic controls that measure wheel slippage at all four wheels independently during acceleration, braking and adverse road conditions.  

Brakes on the STS are up to the car's potential, with a firm pedal and a feel that's reassuringly linear.   All of the various performance packages include four-piston Brembo calipers, with quite large vented brake rotors both front and rear.  

The Lane Departure Warning system engages above 35 mph.   A green light indicates that the system is turned on and working.   Should the driver cross a detected lane marking without signaling, the light flashes amber while an alarm beeps three times.   The system is designed to alert the driver to take appropriate action to move the vehicle back into the correct lane.   To avoid nuisance alerts, the system is designed to not provide an alert if the turn signal is on or if the driver makes a sharp maneuver.   The driver can switch it off, in which case the light goes out entirely. The Side Blind Zone Alert system uses radar to sweep an 11-foot zone on either side of the vehicle; in other words, about one lane over.   The zone starts at each side mirror and reaches back about 16 feet.   With the system engaged, an amber symbol lights up in the outside mirror whenever another vehicle enters this blind zone.   Cadillac cautions that the system is not designed to detect vehicles outside the side blind zone that may be rapidly approaching, or pedestrians, bicyclists or animals.   It's designed to ignore stationary objects, such as fire hydrants or parked cars.   In addition, the system displays do not come on while the vehicle is approaching or passing other vehicles.  

The V6 and V8 engines represent the latest GM thinking, with double overhead cams, four valves per cylinder and variable valve timing.   Called VVT, this system continuously varies valve operation to generate the most power from the least amount of fuel with the lowest emissions possible.   Torque is what most of us experience as power in everyday driving; torque is what gets a car moving in the first place, as when accelerating from an intersection.   Recognizing that, Cadillac engineers designed the STS engines to generate lots of torque throughout the rev range for responsive performance at all engine speeds.