Insider interview on the new 911 Turbo

_L5I6529_L5I6598_L5I6572The next issue of Total 911 will have a massive feature and road/track test of the new Turbo. As a taster, though, here’s an interview with some of the key technical people behind a car that’s more different than first impressions might suggest.

Written by Richard Aucock

“You influence the whole steering behaviour of a car at the rear,’ Product Line Director August Achleitner explains. “Particularly on a 911, where there’s so much weight. With 300kg, it’s the most important axle in the car.

“We’ve always had mechanical traction from it; now, it helps steering, too.” This is torque vectoring in action, his colleague Franz Enderle says. “It’s integrated from the PSM software; it monitors vehicle behaviour in milliseconds, so is very fast to respond.” In essence, it creates a torque difference in the rear axle, by braking the inner wheel in a corner. The outer one, now with extra power and torque, helps create a yaw motion, whose rotational centre is right where the front passengers are sat. Basically, a twist, entirely under the watchful control of computers.

“It’s particularly smart because it’s a ‘free’ system, adding no extra weight,” Enderle continues. “Had we used a mechanical torque vectoring system, it would have added 20kg. Here, all you need is the limited slip differential – just 2kg.

“It took us two years to develop, after thinking long about it. It was done in two stages – first, we had to develop the software, then integrate it into the vehicle.” Surely, we ask, it’s simple enough to be added onto the standard Carrera 4, too? In theory, yes, he admits. “The time comes in integrating it into the vehicle, as every application is different. But I hope if you guys talk about it enough, they’ll let us do it…”

Changes elsewhere seem minimal, Enderle says, but are significant. “Steering hardware is the same, but we’ve optimised the kinematics. The tyres are the same size, but have been further developed. Bridgestone is sportiest; Michelins offer the best ride – and of the 10-second-faster Nordschleif time,  four seconds is from the tyres. The rear subframe is now aluminium instead of steel, something we’ve been able to do because of the space saved in using PDK.”

Oh, and on PDK, he says the basic engineering is as in the Carrera, but it’s all been beefed up to handle all this extra torque. ‘There are different materials for the gear sets, and an extra clutch plate. We also changed the shift profile – the torque means fewer downchanges are needed.” He tells us to watch it on the motorway; it resists downchanging from seventh far more than a Carrera’s PDK.

Of massive significance, but easily overlooked, are Active Engine Mounts. New to the Turbo, these have a further big effect on the handling. “Without them, when you corner, the car turns in first, but mass inertia means the powertrain has to catch up – when it does so, it leans hard on the engine mounts, which alters the balance and needs correction.” Stiffen this 300kg mass and there’s none of this – so, better control, more accuracy and a more ‘together’ impression. They’re standard with the £2629 Sports Chrono pack.

“There are many little points, all of which combined to create a completely different feel. In development, you can be guilty of thinking something’s so small, it doesn’t matter. It does, though. That’s why we fight for every little change.”

Just as significant are the gains of his engine colleague, Martin Kerkau. Porsche remains the only car manufacturer to produce a variable-geometry petrol turbocharged engine. Why? Well, under load, diesel turbos get red-hot. That’s around 800 degrees Celsius. Petrol engines, by comparison, go up to 1000 degrees Celsius – and that’s white-hot.

“You need to ensure the coefficient of expansion is not too great – otherwise, the variable vanes will expand too much and become ‘stuck’ in the turbo. Then there’s the thermal shock risk – if you lift off, cool exhaust gasses create a huge temperature gradient in the turbo.

“To cope with all this, we use aerospace materials, the only ones up to the job. Other manufactures have tried to do what we’ve done, but so far, nobody has managed it.”

What about the incredible noise? All engineered in, Kerkau says. There’s an entire sound engineering department, which have configured the air filter, the air recirculation valves, the exhaust silencer, all to create flow ‘noise’. Tricks include tiny felt pads inside the silencer, and a flow-optimised air filter with intricately modelled openings.

Achleitner points to further incremental gain. The dry sump’s oil tank is now fully built in, sitting where a regular wet sump would sit. Saving 4kg alone, this joins other advances in the all-new engine, to save a total of 10kg – and, more significantly, lower its centre of gravity.

Direct Fuel injection benefits include better response and agility, says Kerkau. Correctly-mixed fuel enters the combustion chamber directly in response to the throttle, so has immediate effect. “Of course, this helps reduce turbo lag.

“It also atomises the fuel more finely, through multi-hole injectors; this evaporates faster in the combustion chamber, creating a cooling effect. We enhance this with the expansion intake manifold – together, they’ve allowed us to safely raise the compression ratio, from 9.0:1 to 9.8:1.”

Reduce boost, too. Yes, despite now having 500bhp, the Turbo now tops at 0.8bar, or 1.0bar on overboost. Before, it was 1.0 and 1.2. Doing this, says Kerkau, means more direct response, more efficiency, and the need for bigger rear tailpipes to handle this extra volume of air rushing out. The exhaust system is lighter, mind, despite the larger cats that allow it to meet the toughest Euro 5 emissions standards.

Economy is up to 16 percent better because of all this – no rival is more fuel efficient. The PDK coupe can return up to 24.8mpg. Truly amazing.

“We haven’t forgotten comforts either,” says Achleitner. “New air-cooled seats suck air through to chill torsos [and their internal fans create a sound-effect not unlike an original air-cooled Turbo’s fan!]. There’s PCM3 navigation, with touch-screen interface, plus that new, small, tactile three-spoke Sport steering wheel with PDK paddles behind.

The paddles are coming to the rest of the Porsche range next year – but, if you want it, you’ll have to go without stereo or phone controls on the steering wheel. “Our aim is to keep design purity,” explains Achleitner. If you want buttons and controls, it’s PDK button control for you. Really, it’s no hardship, I say. His grin shows he agrees.

Look out for the full feature in the new Total 911 – on sale 2nd November, before any of our competitors!

What’s more, you can put your questions on the car directly to Richard Aucock here.

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