The normally aspirated 2.9-liter inline-6 provides good response and acceleration. Volvo says this engine, EPA-rated at 20/28 mpg City/Highway, can propel the S80 from 0 to 60 mph in 8.3 seconds.

With its more powerful engine, the T6 is a rocket. Mash the throttle and the response is instantaneous. It has lots of power at the low end, enough to light up the front tires, assuming you've pressed the STC button to shut off the traction control. The S80 T6 can accelerate from 0 to 60 mph in less than 6.5 seconds, quicker than a Lexus LS430 and much quicker than an Acura RL. The twin-turbocharged T6 engine develops 280 foot-pounds of torque at just 1800 rpm, and maintains it up to 5000 rpm. More torque at lower revs means stronger power for accelerating away from intersections or making passes on long, steep grades. Variable-valve timing enhances the performance of Volvo's T6, but most of the credit belongs to its two small turbochargers, which feed three cylinders each. Two small turbos spool up more quickly than one larger unit, delivering maximum thrust at low rpm. As a result, the T6 is quite responsive when cruising at moderate speeds, say 25-50 mph. Leave the traction control system turned on when you stand on it, and the computer steps in to ensure the front tires lose their grip only momentarily.

The four-speed automatic transmission shifts smoothly and precisely, most notably at higher loads. But occasionally at lower speeds, a quick stomp on the gas causes it to trip over itself, so that it momentarily bogs down before downshifting, and then lurches as it finally finds the right gear. Using the Geartronic to select gears manually enhances the experience for the driver who likes more sporting dynamics.

Both 2.9 and T6 models ride comfortably. The suspension absorbs bumps effectively, eliminating road imperfections. The S80 rides and handles well even with a full load of passengers and luggage. A new steering gear for 2004 offers more direct feedback and enhances dynamic performance, good whether you're driving to the grocery or galloping through the mountains. (The new gear comes from ZF, the German automotive supplier.)

Handling, whether for smoothness or sport, can be enhanced with Volvo's new Continuous Controlled Chassis Concept. The system, developed with Sweden's Ohlins Racing AB, monitors speed, acceleration and other dynamic forces and then adjusts the electronically damped hydraulic shock absorbers to provide either optimal comfort or sport control, depending on the position the driver selects on a switch mounted on the center console. The system can adjust the shocks up to 50 times in a single second. We found Four-C smoothed out rough railroad tracks and reduced body lean when cornering.

The S80's brakes are easy to modulate for smooth stops. Even without Four-C, the suspension does a good job of keeping the S80 level under hard braking: Nosedive during an 80-mph stop was minimal.