The turbocharger, which provides variable boost in concert with the electronic engine management, manages to squeeze 230 horsepower and 243 foot-pounds of torque out of the small 2.3-liter double-overhead-cam engine, which is an impressive 100 horsepower per liter. This sophisticated turbo has eliminated turbo lag, but that's not to say the power doesn't still come on with a rush, because it does; it can go from lugging to zooming in a heartbeat. And it's not strictly rpm-dependent; throttle position has a lot to do with it when the power comes on. For this reason, you can often predict the immediate future by the turbo boost gauge, rather than the tach. Sometimes it kicks in near 3000 rpm and other times it's closer to 4000. It's usually best to give it gas gradually, and don't hammer it.

You can be pulling onto a crowded freeway, looking for holes, and lingering comfortably at 65 mph in third gear (ignoring that upshift light), and when you make your move you're gone. If you're in fifth gear, which is way too tall for acceleration at 55 mph, you won't have the squirt you need. If you drive in a very relaxed manner, it will be easy to get caught in too high of a gear. In that way, it's not unlike a Japanese four-cylinder motorcycle, with a powerband that's way up there.

Acceleration comes in a wonderful and exhilarating surge. If the pavement is irregular you can feel the front end get light, and the front-wheel-drive torque steer twisting the steering wheel as it does. It's a good thing traction control is standard.

You have to be careful, because you can find yourself going faster than you expected in a very short order. The overall acceleration isn't mind-bending, as the quarter-mile time with the five-speed gearbox is in the low 15-second range, but that turbo tends to shoot you off.

The Aero is really at home in smooth twisties. It's so much fun to accelerate at the apex of a turn and feel the car pull you around the rest of the way, as the chassis and suspension hug the road. In a smooth turn that's not too tight, it feels like it's on rails, although sharp turns with a lot of power might push things.

The Aero chassis is lower by 0.4 inches than that of other 9-5 models. The antiroll bars are beefier, the springs and shocks stiffer, and there are firmer bushings in the suspension arms and links, all to minimize body roll and improve steering precision. The changes are a clear success, as the Aero's handling is vastly improved over the other 9-5 sedans.

Same goes for the four-wheel disc brakes, which offer stopping from 60-mph in a mere 120 feet. The front discs grow to 12.1 inches from 11.3 on the other 9-5s, and a different friction material is used for the pads.

Not unexpectedly given the nature of the Aero, the ride is pretty firm over quick light bumps. Generally, the chassis jounces up down a noticeable amount. It's not sharp and not really uncomfortable, but if you peek out the corners of your eyes to the edges of the windshield, you can see the bouncing. The steering remains very steady through this, although less so when the power is on.

The engine has a revvy sound, unfortunately so subtle that you can't hear it with the windows down and sunroof open.