While the limited-edition 959 was Porsche's first AWD production car, the 1989 964 Carrera 4 was the first production 911 to feature four driven wheels. Since then, there's been a Carrera 4 in every 911 range. And while the rear-engined configuration of the 911 gives it an inherent RWD traction advantage over its rivals, there are times when having the front axle driven provides a further advantage. This is certainly true with the turbocharged models, which have used AWD since the 993 Turbo from '95.

Not all the AWD Porsches are born equal. Looking back, it's clear that power sharing between the driven axles has steadily improved over the years. And while some manufacturers consider AWD to be purely a traction aid, Porsche has always looked at it as a performance aid.

The 997 Turbo used a Getrag front differential in combination with a ZF locking diff in the rear. But real advancement came from the electronics that control these diffs, using an ECU in conjunction with sensors that input acceleration, braking, lateral g, yaw and available grip to apportion the right amount of power to each wheel.

Porsche learned more about AWD with its foray into the SUV market. The Cayenne's technology has found its way into the drive systems of the 997 and new 991 Carrera 4 and 4S models.

The latest improvements allow even more precision through electronic control. "If a situation requires 35 lb-ft of torque to the front axle, you will get 35 and not 30 or 40," explained Ulrich Morbitzer, Head of 911 Chassis Development.

The rear-driven 991 Carrera has already carved itself a solid reputation for being the best handling 911 ever, even in the wet. Thus, it was hard to imagine how sending power to the front axle could further improve its dynamic ability other than on slippery surfaces. Given the tendency of a driven front axle to corrupt steering feel, we were afraid the new Carrera 4 might prove to be a less inspirational drivers' car than it rear-wheel drive sibling.

The good news is there doesn't seem to be a downside. From behind the wheel, you feel a little more heft in the Carrera 4's steering, but that's a good thing overall. Other than that, the new model drives exactly like its RWD counterpart on a dry road.

It's available in both Coupe and Cabriolet form, in either the 350hp, 3.4-liter Carrera 4 version or the 400hp 3.8L Carrera 4S.

Despite the warm Austrian autumn weather, we found some damp tarmac under a canopy of trees through a forest. With no traffic in sight we tried a standing start in first gear. On the slippery surface, the Carrera 4S briefly spun all four wheels before hooking up and spearing forward, its diffs and electronics seamlessly finding the optimum grip. Point proven!

A neat feature is the torque split display on the multi-function screen to the right of the rev counter. When you're running on light throttle or coasting, you can see the power go to the rear wheels. Accelerate hard, and the split moves to evenly load both axles.

Ever since the 993, the major distinguishing feature of the Carrera 4 has been its wider rear fenders, and this continues with the 991. The new model is 20mm wider to cover 10mm wider rear wheels.

The rear track width is increased 42mm on the Carrera 4 and 36mm on the S model due to slightly different offset of the latter's 20" wheels versus the 19s on the base model.

The other distinguishing feature is the light strip that joins the tail lights. However, this time it's relatively slim. Less prominent clues are two black horizontal slats on the front air intakes and the black lower sill panels.

Under normal conditions, the dynamic advantages of the new Carrera 4 over the RWD models are less than before, and only shine on slippery surfaces. However, the more purposeful stance created by those wider fenders will look good 365 days of the year.

The new 911 Carrera 4 will launch in early 2013. It will have a base price of $91030, with the 911 Carrera 4 Cabriolet starting at $102930. The 911 Carrera 4S is priced from $105630, or $117530 for the Cabriolet version.

2013 Porsche 991 Carrera 4S

Layout rear-engine, AWD

Engine 3.8L flat-six, DOHC, 24v, variable valve timing

Drivetrain seven-speed PDK dual-clutch or seven-speed manual

Brakes four-piston calipers and 330mm rotors f & r

Suspension MacPherson strut, transverse links, active dampers f, multi-link independent with five arms per side r, PASM

Wheels & Tires 19x8.5" f, 19x11" r, 235/40 ZR19 f, 295/35 ZR19 r

Exterior active rear spoiler

MSRP $105630

Performance

Power 400hp at 7400rpm

Torque 325 lb-ft at 5600rpm

0-62mph 4.3sec (with Sport Plus & PDK)

Top Speed 186mph

Weight 3230 lb (dry)

Economy 18.5/33.6mpg (city/highway)

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