The least costly of Porsche's 911 stable gets its motivation from "right-sizing".

For four decades a Porsche 911 with a turbocharged engine was special enough to deserve a capital "T".

To the many fans of the rear-engined German sports car with its trademark flat-six engine, Turbo came to mean highest power and highest price.

But this is about to change.

From March there will be turbo power in the least costly 911 models of all, the Carrera and Carrera S.

These lower-case Porsche turbos are $200,000-plus cars but they're at least $100,000 less than their range-topping Turbo equivalents.

The mostly new twin-turbo 3.0-litre engine developed by Porsche for the Carrera and Carrera S isn't designed to rival the thumping 3.8-litre of the Turbo. Instead, it's intended to better both the efficiency and power of the 3.4 and 3.8-litre non-turbo engines in the current Carrera and Carrera S.

Maximum power of the 3.0-litre is 272kW in Carrera specification and 309kW in Carrera S form, in each case a 15kW increase over the non-turbo engines they will replace.

The only physical difference between the versions is a tiny increase — just 2mm — in the diameter of the S's turbo compressors. Otherwise they're identical, says Porsche's flat-six engine development director Thomas Wasserbach.

Porsche prefers to call what it has done "right-sizing"

Testing by Porsche in real-world conditions shows that the new engines use from 0.5 to 1.0 litre less fuel to drive 100km, he adds.

When mainstream car makers choose a smaller turbo engine to improve fuel efficiency the word they use is "downsizing". Wasserbach says Porsche prefers to call what it has done "right-sizing".

The company didn't want to lose the instant response when the accelerator pedal is pressed, he says — it's a key ingredient of the 911's sporty appeal — and for this reason, engine capacity wasn't drastically reduced.

Even before the turbochargers can begin to pump up the power, the new 3.0-litre delivers a hefty shove in the back and the first drive dispels any doubt about the 3.0-litre being a 911-worthy engine.

It revs almost as high as the current non-turbo engines — 7500rpm against 7800rpm — and has noticeably greater punch low down. It is quiet when driving slowly and going easy on the accelerator but still has a proper Porsche wail when wound out.

Best of all, the new engine delivers stronger performance. The Carrera S with Porsche's optional PDK double-clutch seven-speed auto and $4790 Sport Chrono Package (which adds launch control technology) is the first of its kind that can accelerate from rest to 100km/h in less than four seconds. Most Australian 911 buyers choose the Carrera S with PDK, by the way.

This is the version CarsGuide spent most time in at the international launch of the updated 911 line-up in Tenerife. The new engine is just 17kg heavier, not enough change the way the Porsche handles.

The steering is as precise as a laser-guided bomb

There are more standard goodies, among them Porsche's PASM adaptive shock absorbers. Ride height is reduced by 10mm.

The Porsche's roadholding is truly awesome. And it needs to be; the new twin-turbo six slingshots the car to silly speeds on any straight, the engine howling like some kind of mechanical animal as it nears the redline.

The brakes feel strong enough to stop a small war, and the steering is as precise as a laser-guided bomb. Most impressive, though, is the way the Carrera S practically explodes out of a corner.

Going to turbo power has affected the way the 911 looks more than the way it drives. Porsche exterior design chief Matthias Kulla says his team examined a dozen ways to get air flowing to all the right places in the rear end, ultimately selecting one of the simplest solutions.

From the rear, the new air-intake grille with its prominent ribs is the easy way to identify the Carrera. Behind it, a new active spoiler does double duty, directing air to the turbo intercoolers as well as generating road-gripping downforce.

Just behind the rear wheels are exit ducts for the air that's passed through the intercoolers. They're exactly where Porsche's aerodynamicists told Kulla to put them, says the designer.

At the front, electrically operated louvres control the flow of air through the engine's radiators. These flip closed above 15km/h when cooling isn't required, reducing aero drag and lift. They open in stages at higher speeds.

The 3.0-litre adds about $8000 to $10,000 to the Carreras. With Porsche's updated seven-speed manual, the Carrera is $217,800 and the S $252,800, the Carrera Cabriolet $239,300 and the S Cabriolet $274,300. The PDK automatic adds $5950.

There's a beaut new sports steering wheel and multimedia with Apple CarPlay compatibility.

The new models adopt the automatic post-collision braking already in many cheaper cars built by the Volkswagen Group, Porsche's owner.

But some items that should be standard in something costing as much as these Porsches are optional, such as adaptive cruise control.