Porsche reveals more turbo 911 details

Porsche has rolled out a few more details about the turbocharged ‘991.2’ 911 Carrera and S Coupes and Cabriolets ahead of a technical briefing today (Friday) and a formal launch at the Frankfurt motor show next Tuesday.

Of course we’ve already reported the essentials of the switch from natural aspiration to a new bi-turbo 3.0-litre boxer engine for the iconic rear-engined German’s ‘entry-level’ models, including power, performance, fuel economy and pricing in place for its Australian launch next March.

But technical details were scarce to say the least and although this second tranche of information doesn’t reveal the whole picture, it does at least lift the curtain a little more.

The latest info reveals the new 911 has actually inched up in weight. Claimed minimum kerb weight of the 991 at launch in 2011 was 1380kg, but the 991.2 weighs in at a minimum 1430kg. There is no explanation for that as yet.

There is a certain symmetry in the 911 Carreras making the shift to turbocharging with a 3.0-litre boxer, because that’s the size of engine the original ‘930’ 911 turbo debuted with in 1974.

That engine made 190kW and averaged 20.9L/100km. This time round, the minimum output is 272kW and fuel consumption goes as low as 7.4L/100km. That’s progress…  

The new engine is an oversquare 91mm bore x 76.4mm stroke, has dual overhead camshafts, four valves per cylinder and a block and cylinder-head constructed of aluminium.

Engine tweaks confirmed by Porsche include:

A new cylinder-head with central injector to improve both combustion and emissions

An adjustable exhaust cam that varies valve timing, joining the VarioCam Plus inlet cam that adjusts both valve timing and lift

A new cylinder wall plasma coating process that reduces friction and fuel consumption

A lighter crankcase chops 1.5kg

A polymer oil pan saves 2kg

Externally, while yet to discuss the turbochargers themselves in any detail, Porsche has confirmed the 911 Carreras require an entirely new airflow system for both combustion and intercooling.

The engine gets its combustion air centrally in front of the rear spoiler, which then flows into the two lower-mounted turbochargers. The heated and compressed air is then fed through two intercoolers located laterally behind the wheel-arches into the induction manifold. The intercoolers are fed cool air via two separate ducts.

Porsche is promising the turbocharged engine and exhaust systems still produce a great sound and has fitted each Carrera model with an individually tuned ‘sound duct’ to pipe induction noise into the cabin.

The standard exhaust is a silencer with two oval tailpipes, while the Carrera S has two integrated exhaust flaps and dual tailpipes. An optional sports exhaust mounts its dual round tailpipes centrally.

Porsche is touting a number of efficiency gains in ancillaries such as the water pump, which now has a clutch controlled by thermal management which leaves it disengaged at low coolant temperatures. In that state the pump draws no power and the engine reaches its operating temperature more quickly. The air-conditioning compressor is similarly controlled.

A two-disc clutch has also been developed for the new generation engine, allowing “comfortable” actuation despite higher torque, Porsche says. More torque has also allowed taller gear ratios from third onwards in the seven-speed manual gearbox for improved economy.

Both manual and the PDK dual-clutch transmission now employ a centrifugal pendulum that absorbs drivetrain vibrations over a broad rev range, allowing smoother use of higher gears at lower engine speeds.

And the PDK shift lever action has been reversed. So pull back to go up and push forward to go down, just like the GT3 racer.

Fuel saving technologies are applied in the form of a coasting function, which idles and then shuts off the engine on descent. The auto idle-stop also interrupts fuel flow sooner when rolling to a stop.

Virtual intermediate gears already used in the PDK of the 911 Turbo are adopted by the Carreras, providing both fuel economy and shift speed gains.