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25 Apr 2019

Lifting the lid on the latest 911 engine

We take a look at Porsche’s latest and most technically advanced turbocharged flat-six

When Porsche unveiled the 992 at the LA Auto Show at the end of 2018, once again we were witness to a new 911 that had grown in every sense. Longer, wider, heavier and laden with all the latest automated driver aids and connective digital assistance. And once again, the next gen 911 promised to be both faster and more efficient. How do they keep on doing it? Porsche is only too keen to tell...
The new 3.0-litre flat-six makes 444bhp in Carrera S trim, with 530Nm of torque available from 2300rpm. That’s a gain of both 30bhp and 30Nm, all through relatively minor fettling, much of it based around the 911’s now universal turbocharging.
It was the second iteration of the 991 that first introduced turbos across the range, no longer the exclusive privilege of flagship performance models. This was a means to reduce engine emissions without sacrificing on poke. It worked of course, even if it was, for the purists, at the expense of a bit of top-end drama. The trade-off was vast reserves of readily accessible torque and with that an easier, more rounded day-to-day driver’s car.
The 992’s engine is fundamentally unchanged from the 991, but the little things Porsche’s engineers have tweaked and revised combine to deliver more for less. For starters, it now features a lighter aluminium crankcase and cylinder head with improved flow to both inlet and exhaust ports. Its VarioCam Plus valve timing has reconfigured the inlet valve lifts to be different on each cylinder. An asymmetric valve lift, Porsche’s engineers explain, means the air intake is displaced at low speeds and loads into an additional swirl flap to improve mixing with the fuel.

This reduces consumption and thereby emissions. Combined cycle fuel consumption comes in between 27.2mpg and 28.5mpg on the Carrera S, with the equivalent CO2 emissions recorded at between 205g/km and 208g/km.
Delivering the fuel is a new direct fuel injection system with a piezo injector, the mainstay of common rail diesel technology. Centrally positioned in the combustion chamber, the injection valves can now open and close far more quickly, supplying a finer fuel mist and ensuring precise distribution at up to five times per combustion cycle.
Porsche has also increased the capacity of the turbochargers, expanding the compressor and turbine and redesigning the manifold.
Another clever improvement has been to arrange the turbos symmetrically while opposing both compressor and turbine wheels from one side to the other. This, Porsche says, optimises the flow ratio and reduces that almost imperceptible lag still further. Maximum boost pressure is now 1.2 bar.

In the confined space of the 992’s rear engine bay, those symmetrically positioned turbochargers also improve exhaust flow through the manifold, turbocharger and catalytic converters. Meanwhile, the diameter of the wastegate valve has been increased to optimise heating of the cat, and larger intercoolers are now positioned directly above the engine, significantly improving intake and exhaust efficiency and re-cooling.
Translating all these refinements to the road is a new eight-speed PDK transmission. Again, this is primarily about reduced emissions, with top speed reached in sixth gear and both seventh and eighth acting as overdrives for cruising. But the additional cog also improves ratio matching, according to Porsche, with a shorter first ratio a better match for the turbocharged engine. Leaving no stone unturned, they’ve also equipped the new ’box with a regulated oil pump, which controls the pressure on shifter and clutch to reduce any loss of power.
Improvements have been made to the smoothness and efficiency of the transmission itself, with better performance at high speed and under load by altering the control parameters. A fast shift system automatically engages during manual upshifts via the wheel-mounted paddles or whenever Sport Plus mode is selected, enabling the 992 to hit 62mph in 3.5 seconds, almost half a second faster than the outgoing 991.
So it’s small but ingenious changes making for small but meaningful gains. Even as Porsche’s cars get larger and heavier, they are also becoming faster and more efficient. And with the second phase of the 992 generation due a performance-oriented hybrid drivetrain, this paradoxical formula looks set to stay.

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