Designing to fit the 911 heritage is a big challenge. While it's a sports car, there's also that strong daily-use quotient. Your margin is greatly narrowed," said Grant Larson on Porsche's newest 997 Carrera and Carrera S. Larson, who had designed the Boxster concept and production cars, and supervised the appearance of the new Carrera GT, also penned the lines that make the new 911 seem so Porsche-like.
"My goal was to tighten everything up, to make the whole car look more technical, more precise, more agile. There were things that I wanted to work with, in the graphics of the lights, to tighten the waist, to widen the hips." His work and engineering efforts also reduced drag from 0.30 for the 996 to 0.28 for the base Carrera. "After my first drive, I was really happy. This car drives with all the mannerisms I had in mind when I designed it," Larson said.
Bringing those mannerisms to the road was a daunting task. Beginning in late 1998, a group of 20 people from engineering, styling, pre-development group and sales, began making concept studies outlining their goals. For Stefan Knirsch, powertrain manager, his was clear.
"You always want more power in the next generation of any Porsche," he said. Knirsch and his staff came up with intake and exhaust modifications to the familiar 3.6-liter watercooled flat-six from the 996 that add 5 bhp to reach 325 at 6800 rpm for the "base" Carrera. Torque remains at 273 lb-ft at 4250 rpm. Enlarging cylinder bore from 96mm to 99 but keeping stroke at 82.8mm brought S engine displacement to 3.8 liters. Using narrower, shorter intake manifolds and a two-piece resonance chamber, it develops 355 bhp at 6600 rpm. Torque is 295 lb-ft at 4600. These statistics translate to acceleration from 0-to-60 mph in 4.8 sec. for the Carrera and 4.6 for the S. Porsche quotes top speeds at 177 and 182 mph. This is the first time since 1977 that Porsche has offered two normally aspirated engine variants simultaneously
Acceleration and top speed, of course, are functions of gearing and tire choices. It was Porsche's decision to run 19-in. tires and wheels for the Carrera S that defined what the 997 would be. The S uses 235/35ZR-19 fronts and 295/30ZR-19 rears. The base Carrera now rides on 235/40ZR-18 at front and 265/40ZR-18 in back.
"Grant Larson made his first sketches with wider tires," August Achleitner explained. Achleitner is manager of the 911 Carrera model range. "It became clear that this choice had wide ranging ramifications." These tires increased loads under cornering, acceleration and braking so greatly that they literally destroyed the first prototypes in late 2001. It forced body, chassis and suspension engineers to redesign much more of the car than they anticipated.
Beginning with the unibody of the 996, they developed techniques to weld and glue components. These methods increased body rigidity by 8%. Additional reinforcement and adhesives resulted in a 40% increase in chassis stiffness. Achleitner was one of several engineers boasting that the new 997 was 80% changed from the 996. More than half of that is beneath the surface. Not a single suspension piece is interchangeable. (The 20% unchanged includes things such as the roof panel, the interior rear seats and the 3.6-liter engine block, crankshaft and its pistons.)
The 19-in. wheels forced powertrain engineers to rework the gearboxes. The larger rolling circumference required shorter final-drive gears to make the best use of engine torque and horsepower. This gave Porsche's wizards the opportunity to address other concerns in both the Tiptronic and manual transmissions, shortening the shift linkage and improving and adding synchros on the six-speed, and quickening shifts on the Tiptronic.
The new car with bigger tires brought Weissach's next suspension and handling advance into play. The Porsche Active Suspension Management, or PASM, is standard on the Carrera S and optional for the Carrera. The improved handling this system offered, plus a goal to enhance frontal crash safety, resulted in widening the front track 21mm (0.83 in.) This reduced body sway and increased anti-roll stability.
A new power-assisted rack-and-pinion steering system-Porsche's first for the 911-works through a variable-rate transmission. In the center, the ratio remains at 17.7:1, comparable to the 996. Turn the wheel more than 30 degrees and the 2.98-turns lock-to-lock quickens to 2.62 (13.8:1.) Parking is much easier and low-speed maneuverability is go-kart-like. Porsche also made the steering wheel adjustable by 40mm (1.57 in.) up-and-down and forward-and-aft.