Safety and efficiency drive latest Porsche 911

The 911 has always been a widely admired sports car, but it's also one that's widely mistaken for its forebears and stablemates.

Even Porsche train spotters will have trouble distinguishing a 996-generation 911 from the smaller and mid/rear-engined 986 Boxster if the two cars are viewed from the front. And within its own branch of the family tree, different generations of 911 are difficult to pick, one from the other.

But looks aside, the latest model — coded 991 curiously — is very definitely a new car from the ground up, as the man who has fathered the project and will continue to nurture it through two more generations told motoring.com.au in Frankfurt last week.

August Achleitner holds down the title of Director of Product Line Carrera, but he is affectionately known within Porsche as "Mister 911". During the media preview day in Frankfurt he revealed that the new car is based on a platform that will also underpin the generation of 911 after the new one ('992'?), just as the first watercooled 911 platform provided the basis for both the 996 and 997 series of 911.

According to Achleitner, it was decided as long ago as 1993, when the 996 and the first-gen Boxster, the 986, were both under development, that the successor to the 997 would migrate to an altogether new platform that would support two series of 911. By our estimation that could conceivably take the 911 line through to around the model year 2024.

"At this time we decided that this platform should last for two generations," he said. "Two generations is a good time, because during the production of these platforms there are so many things changing — regulations, crash requirements and so on — that it doesn't make sense to use the platform again, for a third lifecycle."

Achleitner explained that even in the relatively short timespan the 996/997 platform had been in production and on sale (since 1998), the company had seen fit to upgrade the 997 for additional strength and safety. Carrying the platform through for a third generation would have required a further significant weight gain (180kg).

"It makes more sense to take a [clean sheet of] paper and throw away the history... make a new design, a new concept for the new car, which considers all the requirements, just from the beginning. Then you have the chance to design it in a lighter way than the 997."

Ditching the 997 platform in favour of a new platform for the 991 series meant an overall weight reduction between 35 and 40kg. But the development team for the new model has been selective about the way they've cut mass out of the package. Achleitner says that known lightweight materials are not necessarily an easy fix to reduce weight and improve crash safety.

"Our target is to use the right material in the right place," he said. Some materials will deform in a way unintended for specific areas of the car — in side impacts, for instance.

"We could not replace steel with aluminium," Achleitner continued, "because we need much more space for the frames and so on... so we use high-tensile strength steel... in some areas..."

Correct application of materials and platform design has reduced NVH too, according to the Porsche exec. And again, it's a selective procedure, aimed at reducing the unwanted noise without also eliminating the desirable noise.

"Only by new design and new layout do we have the chance to improve all these single parts – and this only makes sense with a new platform.

"By reduction of the noises we can transmit better engine sound into the interior, so that you can hear what you want to hear..."

"In Germany, when you have the chance to go 200km/h, today in the 997 a conversation with your passenger... [is] almost not possible... but it's absolutely not a problem in the new 991."

According to Achleitner, Porsche engineers have focused on the rear of the car, using parts that provide "better damping behaviour". The "most critical point" for noise damping is below the rear window. In fact, wind noise around this area was the key reason for Porsche's decision to make the engine inaccessible from above. There's no longer a conventional engine cover that can be lifted to reach the engine's servicing points, which may be disappointing for owners, but is also a factor in the new model's drag coefficient of 0.29Cd. That not only reduces wind noise, but also improves fuel efficiency.

"[For] access to the engine compartment for service and maintenance, you have to put this car on the hoist..." Achleitner confirmed.

On the hoist is where many owners are likely to notice the difference in length between 991 and its predecessors. The wheelbase of the 991 series has been stretched 100mm; a changed intended to improve packaging more so than ride comfort or handling. In fact, according to Achleitner, the weight distribution has barely changed with the longer wheelbase — to 39.1fr/60.9rr from 39.0fr/61rr of the 997.

Overall the 991 model is just 56mm longer and half that added length comes out of technical requirements and "some concerns for the future", but "the other half is coming from styling and shape".

In part, the longer wheelbase of the 991 series is attributable to Porsche's new seven-speed transmission —a more compact unit than the six-speed box in the 997. The new manual transmission is based on the existing PDK box already introduced with the 997, which was another reason for Porsche to go ahead with the development of this particular transmission. Achleitner explains...

"When we started the development... of the 991, the decision had been open to bringing out the six-speed manual or a seven-speed. During the development phase of the PDK gearbox for the 997, we knew that we had to create the new manual gearbox for the 991 out of the PDK layout, because only the PDK layout allowed [Porsche] to make this [extra] wheelbase. So this additional 100mm of wheelbase — there's an effect of about 70mm coming out of the gearbox layout, which allowed us to place the rear wheels a little bit [further to the rear]."

Achleitner argues that those buyers who don't want to use all seven gears can use the manual just like a conventional six-speed box. Compared with the PDK box, the seven-speed manual has shorter ratios in third and seventh, providing a faster kick-down when required, but also reducing the need to change gear as frequently in the manual.

Porsche has chosen to develop an electrically-assisted steering system for the 991 series car. The advantages of such steering systems are well known — as are the shortcomings. Achleitner claims that Porsche has ironed out many if not all of the system's vices in the new model.

"The variable rack is similar but not exactly the same [as in the 997]. The power steering by itself is now [electrically assisted]."

"The C2 and the C4 have different front axle loads. We can adapt [the steering system] very easily and we can also filter information from the road — information we don't want to transmit to the driver."

By adopting electric assistance for the steering system, the new 911 uses 0.15L/100km less than a theoretical model fitted with the 997's hydraulic setup. The steering ratio for the new system is "a little more direct" says Achleitner. At the straight-ahead it measures 16.6:1 and on hard lock it measures 12.25:1. For the 997 the ratios varied from 17.1:1 at the straight-ahead to 13.76:1.

For many prospective buyers of the 991 series, the proof of the pudding is in the lap times the new 911 can set around the north loop ('Nordschleife') of the Nurburgring. Practically located in the German sports car maker's own backyard, the public-road racetrack has seen Nissan set a new lap record in the GT-R, beating Porsche's previous best time for the 911 in the process. It has been a sore point at Porsche's HQ in Zuffenhausen, but the 991-gen Porsche is ready to take up the challenge once more.

Achleitner throws a lot of qualifications into his estimation of the new 911's time for the Nordschleife. On regular road tyres and with the PDK (dual-clutch seven-speed transmission), 20mm-lower sports suspension and PDCC fitted, the Carrera S has recorded a time of 7:40.

"[That's] nearly the same [time] as the 997 GT-3 car..." Achleitner said, stressing that in different environmental conditions and with a different driver at the wheel a time like 7:36 might be possible.

PDCC (Porsche Dynamic Chassis Control) is an active anti-roll bar system introduced to the 911 with the 991 series, but was first developed by Porsche for the Cayenne SUV. Unlike the Cayenne's system, the 991 series has hydraulic pumps between each end of the anti-roll bar and the mounting point on the strut. The pressure within the pump can be varied automatically, changing the roll stiffness on demand, in effect. It's a lighter, more compact system than that type used in Panamera and Cayenne, but also consumes less energy in operation.

In that regard, it's consonant with many of the changes and new features of the 991-series 911 — all about balancing performance and dynamics with fuel efficiency, comfort and safety.

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