Porsche boxes clever with the new Boxster

  • 31-Aug-2012 04:20 EDT
Porsche Boxster_S_8-12 1.jpg

Compared to previous generations, the new Porsche Boxster is 32 mm (1.3 in) longer on a 60 mm (2.4 in) longer wheelbase with a 6 mm (0.2 in) lower c.g.

Lighter, longer, lower, stiffer, quicker, more fuel frugal, with enhanced dynamics and cockpit comfort all bringing an altogether more “adult” feel; that sums up the new and much improved generation of the mid-engine two-seat Porsche Boxster.

A raw sports car it is not. According to Dr. Manfred Harrer, Porsche’s General Manager Vehicle Dynamics and Performance, Boxster buyers are certainly looking for high performance and striking aesthetics but linked to an equally high level of comfort and ride quality. They do not want a boulevard cruiser and they insist on Porsche’s distinct vehicle design and engineering signature.

It is helping meet these disparate needs that has concentrated the mind of Harrer. In S form, the new Boxster can lap the Nürburgring Nordschleife in 7 min, 58 s, 12 s faster than the previous model from only 3.7 kW (5 hp) more power—and precisely the same time as the very-high-performance 911GT3 of 1999. So a great deal of this achievement is down to the car’s new chassis—the responsibility of Harrer and his team.

Today’s Boxster range comes in regular and S forms. The base model now comes with a 2.7-L (vs. 2.9-L) engine but with an extra 7.5 kW (10 hp), and it offers up to 15% improvement in combined fuel consumption and emissions, particularly when specified with Porsche’s redesigned seven-speed PDK twin-clutch transmission. The S manages 8.0 L/100 km vs. the regular car's 7.7 L/100 km, and it produces 232 kW (311 hp) at 6700 rpm and 360 N·m (266 lb·ft) between 4500 and 58800 rpm.

Its new hybrid (aluminum and steel) bodyshell provides a massive static torsional stiffness improvement of 40% over the previous model; mass is down by as much as 35 kg (77 lb), depending on version, and aerodynamic lift by 17.5%.

The front track is up to 40 mm (1.6 in) wider and wheelbase is stretched 60 mm (2.4 in), providing much needed added space for tall drivers. Overall length increases by 32 mm (1.3 in). The front axle uses a MacPherson system with new lightweight spring struts for precise camber control and aluminum wheel carriers. Use of aluminum saves 2 kg (4.4 lb). The rear axle is multilink with aluminum wheel carriers and enlarged supports and is mounted on a rigid subframe.

Standard or optional features include PASM (Porsche Active Suspension Management), 20 mm (0.8 in) lower PASM sports chassis plus torque vectoring, and PDCC (Porsche Dynamic Chassis Control). The c.g. is 6 mm (0.2 in) lower, and overall height is reduced between 10 and 13 mm (0.4 and 0.5 in).

Singling out one aspect of the Boxster as its most significant technology is a tough call but, said Harrer, referring to the Nürburgring times: “The completely new chassis has a decisive influence on the impressive performance increases.”

A challenge for Porsche is that a chassis has to meet requirements for road and track, he said. “Not just on track but to win on track! But comfort level is very important, and it is very difficult to find the right balance, although electronic systems are increasingly helping towards this.” As does the high torsional stiffness (Porsche was unable to reveal a precise figure) of the diecast and sheet-aluminum-intensive (46%) bodyshell. Steel is used only where it is deemed indispensable. The cockpit holder is of magnesium. Bodyshell stiffness may be further improved. “We have ideas about how to optimize it for the next generation, but we may not see the huge step that we have just achieved with the car, which has taken a lot of engineering,” he said.

Could that mean carbon fiber both in the bodyshell and chassis? Despite industry efforts to drive down the cost of carbon fiber to make it usable for medium-volume applications, Harrer does not see a complete Boxster in the material emerging in the next generation of the car. He is cautious: “It is not too easy to use in the chassis; we are at the beginning of possible use in this area.” Wheels and possibly axles are being discussed, as is the substitution of carbon for steel springs. “But other than these, I do not see any trends although there may be a mix of steel and carbon fiber for some internal components.”

Steering precision and feedback to the driver have been long established Porsche assets. Unassisted systems of the 911, up to and including the 1989MY 3.2 Carrera, were renowned for their precision. The new Boxster has an electromechanical system which reduces fuel consumption by 0.1 L/100 km.

When today’s systems were being evaluated, was reference made to those early cars? Harrer found the question interesting, but felt that today’s tire types and sizes, wheel construction, body stiffness, and suspension details meant a comparison was not possible in objective terms. He also explained that there is now a tendency toward ever higher steering ratios to exploit added chassis capability and to achieve better lane change and slalom test performance. Also important is the diameter, weight, and feel of the steering wheel. At one time, Harrer was responsible for Porsche steering wheel design and development.

The new Boxster gets improved braking with front six-pot aluminum monobloc fixed calipers for the S, a carry-over part from the latest 911.

Tire performance has always been a compromise to give required results for wet and dry grip, noise, and rolling resistance. Latest generation tires for the Boxster provide 3% better braking, 2% improved dry handling, and a similar figure for wet handling. Rolling resistance is better by 7%.

“However, we are at a point where we need to reconcile our strategy. We want to keep our performance levels, but we are now in deep discussion with our tire suppliers (including Michelin, Continental, Pirelli, Dunlop, and Goodyear) about where we go in future regarding rolling resistance. This can be optimized but may not be so good for braking performance. Discussions have now started on the new generation of tires for our cars.”

Discussions are also under way other with suppliers, notably ZF, regarding the next generation of torque-vectoring systems. This is mainly about control algorithms, particularly with regard to the forthcoming Porsche SUV, said Harrer. “All electronic chassis systems need to work efficiently—but avoid unwanted ESP intrusion, with reaction taken to a higher level while providing linear feel to the driver."

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