► We break down the new Porsche engine
► Additional turbo, here’s how it works
► Banishing lag for instant throttle response
When Jörg Kerner, Porsche’s vice president for powertrain development, arrived at Weissach four years ago from Audi, where he developed the RS6’s thundering V8 and the five-cylinder RS engines, he promised his bosses that the new flat-six would be ‘the benchmark for response from a turbocharged engine’.
First impressions of the 991.2 Carrera and Carrera S are that Kerner may just have pulled it off – a downsized, more efficient flat-six with much of its wondrous response and character intact. Here’s how.
1) Light and future-proofed
New engine block is manufactured from hypereutectic aluminium; stiffer, more resistant to thermal expansion and 1.5kg lighter than the old block. Plasma-sprayed iron cylinder liners help reduce fuel consumption and cope better with the poor fuel grades found in India and China. A composite oil pan saves a further 2kg over the previous engine.
Both 2981cc launch engines share the same 91.0mm bore and 76.4mm stroke, 10:1 compression ratio and 7500rpm rev limit. The bore spacing allows for larger capacity engines in the future, naturally.
Maximum power is developed at 6500rpm for both engines, where the naturally-aspirated 991 Carrera S needed 7400rpm on the tacho. Progress? The hairs on the back of your neck may disagree, at least until they feel the shove of torque from just 1700rpm.
2) Banishing the lag
Porsche is being cagey about the six’s patented turbo management system and its electro-pneumatically controlled wastegate. Designed to minimise lag, the Achilles heel of blown engines, it works to maintain optimal turbo speed and pressure. The ECU analyses throttle position and juggles several parameters – the wastegate, ignition timing, the adjustable exhaust camshaft, intake valve lift and duration via the VarioCam Plus system – to provide instant response.
3) High-pressure injection
Each bank has its own high pressure pump for the centrally located injectors, delivering fuel at 250bar, for optimal atomisation, minimal cylinder-wall wetting and low CO2 emissions.
4) On-demand cooling
Smart electronics declutch both the air-conditioning and water pumps when not needed to reduce engine drag. The engine quickly reaches its initial 90°C operating temperature, then settles back to 85°C in normal running, during which the coolant circulates more slowly.
5) Let there be oil
Unlike inline or vee-configuration engines, flat-sixes don’t have gravity to help the engine’s oil flow back to the sump. The 911 boasts a complex lubrication system, not least to keep the low-mounted turbos oil-fed and happy. As well as the main steady-state pump, which provides 2-3bar of oil pressure by means of a variable pump (oil pressure is increased under heavy load and hard acceleration), the engine uses three soak pumps: one for each cylinder head and a third specifically for the two turbos. Each blower as its own oil canister, from which hot lubricant is drained and recirculated back to the sump.
